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Evap Diagnostic Summary P0443 Purge Control Valve Circuit problem P0444 Purge Control Valve Circuit Open • P0445 Purge Control Valve Circuit Shorted • P0458 Purge Control Valve Circuit Low • P0459 Purge Control Valve Circuit High • P0496 Purge Control Va

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Evaporative Emission Control System Diagnostics
Contents
Evaporative Emission Control System Diagnostics ........................................................................................................ 1
Evap System Operation ................................................................................................................................................ 6
DTC Specific Diagnostics .............................................................................................................................................. 6
THINK SAFETY! ............................................................................................................................................................. 6
Evaporative Emission System Introduction ................................................................................................................... 6
Evap System Generations ............................................................................................................................................ 7
Enhanced Evap Systems ............................................................................................................................................... 7
Need for Improved Diagnostics ................................................................................................................................... 7
Statics of Evap System Failures .................................................................................................................................... 8
OBD Diagnostics ........................................................................................................................................................... 8
Equipment for Gas Cap Testing .................................................................................................................................... 8
Check for Codes ........................................................................................................................................................... 9
GM OBDI Example ....................................................................................................................................................... 9
Purge Solenoid Valve ................................................................................................................................................... 9
Purge Flow Sensor ..................................................................................................................................................... 10
Purge Vacuum Switch ................................................................................................................................................ 10
Purge Test Port .......................................................................................................................................................... 11
Evap Vacuum/Pressure .............................................................................................................................................. 11
Evap Test Port ............................................................................................................................................................ 12
Impact of 1 psi ........................................................................................................................................................... 12
Purge Rules ................................................................................................................................................................ 13
Purge Criteria ............................................................................................................................................................. 13
Leak Check Enabling Conditions ................................................................................................................................. 14
Ford’s Enabling Conditions ........................................................................................................................................ 14
Service Bay Evap Self-Test ......................................................................................................................................... 14
Service Bay Self-Test Example .................................................................................................................................... 16
Evap Service Bay test Data ......................................................................................................................................... 17
Monitoring Purge Activity .......................................................................................................................................... 18
Purging a Full Canister ............................................................................................................................................... 18
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Purge Action in Scan Data .......................................................................................................................................... 19
Initial Purge after Restart ........................................................................................................................................... 19
Initial purge Graph after restart ................................................................................................................................. 21
Diagnostics for All Systems ........................................................................................................................................ 22
Example of Code P0440 ............................................................................................................................................. 22
OBDI P0440 for a 1996 GM ........................................................................................................................................ 22
OBDI Evap Component Testing .................................................................................................................................. 23
Evap Component Diagnostics .................................................................................................................................... 23
Purge Solenoid Diagnostics ........................................................................................................................................ 23
Flow meter Testing .................................................................................................................................................... 23
Full Flow and No Flow Indications .............................................................................................................................. 24
Purge Solenoid Resistance ......................................................................................................................................... 24
Purge Solenoid Current Testing ................................................................................................................................. 25
OBDII Purge Valve Codes ........................................................................................................................................... 25
P0443 Diagnostics ...................................................................................................................................................... 25
Current Testing Code P0443 ...................................................................................................................................... 27
Multimeter Amp Testing P0443 ................................................................................................................................. 28
P0443 Diagnostics Resistance .................................................................................................................................... 29
P0443 Diagnostic Summary ....................................................................................................................................... 30
P0444 Code Diagnostic .............................................................................................................................................. 30
Check B+ to the purge solenoid ................................................................................................................................. 30
Purge P0445 Current flow Test .................................................................................................................................. 31
Purge P0445 Resistance Test ..................................................................................................................................... 33
P0445 Diagnostic Summary ....................................................................................................................................... 33
P0458 Code Diagnostic .............................................................................................................................................. 33
P0458 Code Current Diagnostic ................................................................................................................................. 33
P0458 Diagnostic Summary ....................................................................................................................................... 33
P0459 Code Diagnostic .............................................................................................................................................. 34
P0496 Code Diagnostics ............................................................................................................................................. 34
P0496 Current flow test ............................................................................................................................................. 34
P0496 Diagnostic Summary ....................................................................................................................................... 35
Purge Diagnostics Conclusion .................................................................................................................................... 35
Evap Hoses ................................................................................................................................................................. 35
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Evap Vacuum Switch .................................................................................................................................................. 35
Evap Vacuum Switch Testing ..................................................................................................................................... 35
Evap Leak Codes ........................................................................................................................................................ 36
Testing for leaks OBDI ................................................................................................................................................ 36
Testing for leaks using the EVAP Test Port .................................................................................................................. 36
Connecting a Smoke Machine .................................................................................................................................... 38
Select a Point to Test ................................................................................................................................................. 39
OBDII with a Vent Seal Solenoid ................................................................................................................................ 39
Typical Vent Seal Application ..................................................................................................................................... 40
Sealing the system with the vent solenoid ................................................................................................................. 41
Bi-directional control with a scan tool ........................................................................................................................ 41
Service Bay Evap Test ................................................................................................................................................. 43
Vent Seal Solenoid Circuit .......................................................................................................................................... 44
Calibrating the Flow Gauge for Leaks .......................................................................................................................... 45
Use the Smoke ........................................................................................................................................................... 46
Purge with a Vent Open ............................................................................................................................................. 48
Vent Seal Solenoid Codes .......................................................................................................................................... 48
Code P0446 ................................................................................................................................................................ 49
Code P0447 ................................................................................................................................................................ 50
Low Amp testing ........................................................................................................................................................ 51
Code P0447 Summary ................................................................................................................................................ 52
Code P0448 ................................................................................................................................................................ 52
Code P0449 ................................................................................................................................................................ 53
Restricted Vent Solenoid ........................................................................................................................................... 54
Code P0498 ................................................................................................................................................................ 55
Current flow testing ................................................................................................................................................... 55
Code P0499 ................................................................................................................................................................ 56
Code P0499 Flow Restriction Test ............................................................................................................................... 56
Code P0499 Voltage Test ........................................................................................................................................... 56
Code P0499 Summary ................................................................................................................................................ 56
Fuel Tank Pressure Sensor Codes ............................................................................................................................... 57
FTP Code Diagnostics ................................................................................................................................................. 57
FTP Sensor Voltage Test ............................................................................................................................................. 57
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GM Scan Data Recording ........................................................................................................................................... 58
System Specific Operation ......................................................................................................................................... 58
Evap Pressure Vacuum Decay .................................................................................................................................... 58
Vacuum Decay Leak testing ....................................................................................................................................... 59
Evap Monitor Vacuum ............................................................................................................................................... 59
First Phase of Vacuum decau test ............................................................................................................................... 60
Mode 6 for Purge monitor ......................................................................................................................................... 60
Mode 6 for Honda Purge monitor ............................................................................................................................... 60
Mode 6 Data Analysis ................................................................................................................................................ 61
Mode 6 Specifications ................................................................................................................................................ 61
Second Phase of Evap Test ......................................................................................................................................... 61
Blocked Purge Hose Test ............................................................................................................................................ 63
Mode 6 Weak Vacuum Test ....................................................................................................................................... 63
Third Phase of Evap Test ............................................................................................................................................ 63
Fourth Phase of Evap Test ......................................................................................................................................... 64
Fifth Phase of Evap Test ............................................................................................................................................. 64
Sixth Phase of Evap Test ............................................................................................................................................ 65
Natural Vacuum Evap Test ......................................................................................................................................... 65
Engine off Natural Vacuum ........................................................................................................................................ 65
Ford’s EONV Phase 0 .................................................................................................................................................. 65
Ford’s EONV Phase 1 .................................................................................................................................................. 65
Ford’s EONV Phase 2 .................................................................................................................................................. 66
Engine off Natural Vacuum Graph .............................................................................................................................. 66
Ford’s EONV Phase 3 .................................................................................................................................................. 66
Ford EONV Mode 6 .................................................................................................................................................... 66
Ford’s EONV Phase 4 .................................................................................................................................................. 67
GM Engine off Natural Vacuum ................................................................................................................................. 67
Chrysler Evap Systems ............................................................................................................................................... 67
Chrysler Leak Detection Pump ................................................................................................................................... 67
LDP in Purge Mode .................................................................................................................................................... 67
LDP Vacuum Applied .................................................................................................................................................. 68
LDP Self-Test .............................................................................................................................................................. 68
LDP Lab Scope Testing ............................................................................................................................................... 70
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Normal LDP Duty Cycle Signal .................................................................................................................................... 70
Large Leak Duty Cycle Pattern ................................................................................................................................... 70
Leak Detection Pump Mode 6 .................................................................................................................................... 70
Chrysler Natural Vacuum Leak Detection ................................................................................................................... 71
Chrysler NVLD Operation ........................................................................................................................................... 71
Chrysler NVLD Mode 6 ............................................................................................................................................... 73
Chrysler ESIM ............................................................................................................................................................. 73
ESIM Action ................................................................................................................................................................ 74
ESIM Pressure Relief .................................................................................................................................................. 75
Natural Vacuum Action .............................................................................................................................................. 75
Developing a Vacuum ................................................................................................................................................ 75
Chrysler ESIM Diagram .............................................................................................................................................. 76
Model Specific Application ........................................................................................................................................ 76
ESIM Natural Vacuum Results .................................................................................................................................... 77
Toyota non-Intrusive Evap ......................................................................................................................................... 77
Toyota Air Drain Valve ............................................................................................................................................... 77
Toyota Air inlet Valve ................................................................................................................................................. 77
Toyota Vapor Switching Valve ................................................................................................................................... 77
Non-Intrusive System Testing .................................................................................................................................... 78
Toyota Intrusive Evap ................................................................................................................................................ 78
Toyota Bypass Valve .................................................................................................................................................. 79
Toyota Key off Evap Test ............................................................................................................................................ 79
Key off Evap Timing Chart .......................................................................................................................................... 80
DM-TL Evap System for Imports ................................................................................................................................ 82
DM-TL Evap System Orifices ...................................................................................................................................... 83
DM-TL Evap System Test ............................................................................................................................................ 83
DM-TL Pressure/Current Chart .................................................................................................................................. 83
Evap Diagnostic Summary .......................................................................................................................................... 84
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Evap System Operation
Technicians will have an in-depth understanding of the differences in Evap monitor testing techniques.
Evap systems to be covered are:
 EVPD
 EONV
 LDP
 NVLD
 ESIM
 Toyota Non-Intrusive
 Toyota Intrusive
 KEY-OFF
 DM-TL Evap System For Imports
DTC Specific Diagnostics
Technicians will use equipment for efficient diagnostics.
 Testing with scan tools bi-directional control
 Testing with digital multimeters
 Testing with flow meters
 Testing with smoke machines
We are going to use a smoke machine with a flow meter to check for restrictions and leaks, smoke is part of our testing but not everything.
THINK SAFETY!
Be careful when using shop air for Evap testing.
Adding air to the fuel tank creates a highly combustible mixture.
The use of nitrogen or CO2 as a purge gas is highly recommended.
Do not perform tests near a source of spark or ignition.
Fires can be caused by arching wiring and connectors on the vehicle.
No open flame heaters or other sources of ignition in shop area
Evaporative Emission System Introduction
In 1978 the EPA issued rules that evaporating fuel vapors must be absorbed by a charcoal canister and then released into the intake manifold.
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Evap System Generations
After the introduction in 1973, evaporative emission systems have undergone numerous changes.
Early systems had limited diagnostic codes, usually dealing with electrical operation of solenoid and switching valves.
We will develop diagnostics that can be applied to all systems as we go through the various Evap systems.
Enhanced Evap Systems
The evolution of OBDII enhanced evaporative emission systems complicated Evap diagnostics.
Enhanced Evap systems have improved leak detection.
1996-1999 enhanced systems can identify 0.040” leaks. Some vehicles were granted waivers initially.
2000 and newer enhanced systems can identify 0.020” leaks.
Need for Improved Diagnostics
Detection of 0.020” leaks has increased the frequency of diagnostic trouble codes for leaks.
0.020” leak codes are more difficult to locate in many cases.
4 pin hole size leaks, the size of an average human hair, can be detected by the 0.020” leak check.
Some repairs become difficult when the cause is several small leaks
Technicians need to verify the repair and correct all the issues before returning the vehicle to service.
Evap systems diagnostics require detailed understand of how different Evap systems operate.
We are going to use diagnostic procedures for most of the evaporative system diagnostic trouble codes.
We are going to use a testing approach that is efficient enough to allow testing after a repair.
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Statics of Evap System Failures
OBD Diagnostics
OBDI Evap diagnostic could not detect minor leaks like a fuel filler cap.
A good diagnostic starting point for an enhanced Evap system would be to check the filler cap early in the diagnostic. Just remember, it will not correct an OBDI code.
Filler caps can be tested or replaced
22.8% of the failures are filler caps and it is easy to check, but don’t assume it is the problem because it is a frequent failure.
If you want to try a replacement filler cap; the system must be checked before and after replacement to measure any improvement. We have a procedure for checking and measuring results. Evap codes are a frequent reason for a comeback after repair.
Equipment for Gas Cap Testing
There are testers for fuel filler cap to make testing easy. Filler caps are a frequent problem but do not forget the filler neck, a good cap cannot seal a dented filler neck.
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Check for Codes
Diagnostic codes are the usual reason for checking the Evap system.
Codes point us toward the problem area as a likely cause of the problem.
Examples of codes for OBDI and some OBDII Evap systems:
 P0440- No flow detected when the Evap monitor attempted to purge the system (OBDI) or failure to pull a vacuum.
This code definition changes with different generations of Evap monitors. Some OBDI vehicles use a flow sensor that responded to purge flow. OBDII vehicles usually use a sealed system test that can locate smaller leaks.
This is an example of how diagnostics change with different generations of Evap monitors. We will start with an OBDI diagnostic for GM as an example.
The OBDI code indicates no flow was detected by the flow sensor, when the purge solenoid was energized.
We will walk through the functions necessary to have normal flow through an OBDI flow sensor.
GM OBDI Example
Purge Solenoid Valve
The valve may be called Purge solenoid, Purge valve, Canister valve, Vacuum switching valve.
Purge Valve must apply vacuum to the canister when energized. Restrictions in the canister or hoses can
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prevent purge flow. Canister must not be clogged with water or debris.
Purge Flow Sensor
The purge flow sensor closes a switch when vacuum is applied to the purge system.
Purge Vacuum Switch
Purge vacuum opens the vacuum switch to indicate purge is operating
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Purge Test Port
Purge flow sensor closes a switch when vacuum is applied to the purge system.
Evap Vacuum/Pressure
Evap pressure and vacuum values are very low. They are measured in inches of water. Pressure is also measured in inches H2O, 1 psi is 27.67 “H2O. Automotive vacuum is measured in inches of mercury.
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Evap Test Port
Limit the vacuum or pressure applied to the test port.
Maximum pressure is 1 PSI!
Evap vacuum is frequently referred to as a weak vacuum to remind technicians a normal automotive vacuum gauge scale is too large to measure the low vacuum levels of an Evap system.
Impact of 1 psi
1 psi is 1 pound per square inch of surface area.
1 psi of pressure applied to a 10 by 10 inch area of a fuel tank is 100 pounds.
Apply this force
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to all the square inches of a fuel tank and the force is very high.
Do not apply high vacuum or air pressure to the test port because fuel tank damage could occur.
Tank cars can be crushed by vacuum if they are pumped out the pressure/relief valves are disabled.
Purge Rules
The PCM has specific strategies to manage fuel delivery during purge.
 Initial purge opening will limit the amount of vapor flow.
 PCM monitors short term fuel trim to determine fuel vapor concentration.
 Purge must not cause an engine performance problem.
The PCM lowers the duty cycle when vapor concentration is high.
Purge Criteria
Normal purge takes place after engine is warm up usually 140⁰ to 160⁰ F, but stops during wide open throttle.
Short term fuel trim will shift negative, to correct for a rich mixture, when fuel vapors are present. The PCM will make fuel adjustments to compensate for fuel vapors from the canister. The duty cycle will increase as the fuel vapors are cleaned out of the canister.
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Leak Check Enabling Conditions
Vehicle conditions necessary to allow an accurate measurement of leaks also needs rules.
Enabling conditions are necessary because some conditions make leak detection difficult and unreliable.
 Vacuum decay systems pull a weak vacuum on a sealed system and measure the time it takes for the vacuum to “leak down”.
The PCM must compensate for fuel temperature to time the vacuum decay.
Warm fuel has a higher evaporation rate than cold fuel would have.
The PCM uses the assumption that the fuel is approximately the same as coolant temperature after 6 to 8 hours without engine operation.
 The PCM will delay running the Vacuum decay leak check for 4 to 6 hours after shut down.
 Fuel temperature must be in a specific range to perform a vacuum decay leak check.
 Usually the temperature requirements are in the range of 40⁰ F to 95 ⁰ F at start up after the engine off time requirement.
 The fuel level must be in the mid-range that varies slightly but usually 15% to 85%.
 These requirements are sometimes responsible for a rash of Evap codes in late winter or early spring when the weather is above 40⁰ F.
Ford’s Enabling Conditions
These enabling condition are typical conditions required by all vacuum decay leak detection systems.
Service Bay Evap Self-Test
A 0.040” Evap Self-test is required after model year 2007.
Most scan tools run this under special test or bi-directional testing menu.
Some vehicles have a waver to provide a limited version of this test, so don’t expect every vehicle to do the service bay test. The vehicles with the exception may run a quick test in the first few minutes of a test drive or have specialized manufacturer specific test.
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Service Bay Self-Test Example
Select special tests or Test On-board Systems.
Start the test.
The PCM will take control of engine speed and run the 0.040” leak check that is done with the engine running.
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Evap Service Bay test Data
The AutoEnginuity Scan Tool shows data.
Test Results;
Most scan tools also provide Bi-direction or activation functions that are very useful for testing Evap systems. The function allows technicians to control actuators and PCM functions. We will use these Bi-directional controls to open and close the vacuum control valves during our Evap testing.
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Evap Bi-Directional Test
This is an AutoEnginuity example of bi-directions testing
.
The control of the vent and purge valves will be used during code diagnostics to increase efficiency. The increased efficiency will enable us to testing before and after a repair to measure improvements.
Monitoring Purge Activity
We are going to use scan data to measure the data used to control canister purge. Purge should not cause an engine performance problem. The PCM will correct for fuel vapors in the purge air to prevent causing a performance problem.
Purging a Full Canister
Purge starts quickly after a refueling event because the canister has captured refueling vapor. The purge air will have high fuel vapor content after refueling.
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Purge Action in Scan Data
The PCM opens the purge solenoid slowly and monitors short term fuel trim.
The increase in purge flow in this example causes the oxygen sensor signal to go rich.
Short term fuel trim will go in the negative direction to keep fuel delivery normal.
Initial Purge after Restart
Canister purge starts slowly until the PCM can determine the fuel vapor level in the purge flow. In the example
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we recorded the purge duty cycle as it goes from 0% to 12% to check the fuel content of the purge air flow. We added fuel tank pressure to this recording. This is the format we will use later to check for a restriction in the Evap system.
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Initial purge Graph after restart
The change in short term fuel trim is used to manage fuel injection and purge duty cycle. STFT dropped from about +2.3% down to -3.1% when Purge started.
The start of purge does not change fuel tank pressure readings indicating low restriction in the system.
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Diagnostics for All Systems
The diagnostic codes for OBDI will be covered as we address OBDII. The purge solenoid and hoses will be diagnosed the same way on OBDI and OBDII. A 0.020” leak may be more difficult to locate but the procedure will be the same as checking for a larger leak. The second version of leak testing will cover systems with a vent seal solenoid that is not used on OBDI. Then we will cover the unique systems for different manufacturers separately.
Example of Code P0440
We will use P0440 for the OBDI example. We will always use manufacturer specific Evap diagrams during the diagnostics because there may be fuses and other differences that must be addressed. We will test each part of the system to locate the cause of the code. An OBDI code indicates no flow was detected. The cause of no flow could be any of the components in our Evap example.
OBDI P0440 for a 1996 GM
Normal purge causes a slight vacuum in the system if everything is normal. The slight vacuum closes the flow sensor switch when tank purge is started indicating normal purge flow. The OBDI version has limited leak checks. A leak must be large enough to reduce the vacuum to a value below vacuum needed to close the flow sensor.
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OBDI Evap Component Testing
We are going to use test procedures for Evap components that can be used for most Evap systems. Some systems will use modified testing that will covered separately in the manufacturer specific section.
Purge valve- Used by all systems.
 Check for flow and sealing action.
 Check electrical operation
 Hoses-Used by all systems.
 Select test points to localize the area with the leak.
 Test Port- Used on most systems.
 Connection for test equipment
 Pressure and flow indications
Evap Component Diagnostics
We will use aftermarket tools to diagnose Evap components. Sometimes manufacturer diagnostic instructions refer to factory special tools that may not be available to everyone.
Purge Solenoid Diagnostics
The diagnostics we use here can be used on most Evap systems.
We need a quick and accurate test that can be repeated after a repair to confirm the repair effectiveness.
Ford has a Vapor Management Valve, but the function was similar to duty cycle purge valves. Ford VMV is controlled by current, which is available in scan data
We need to answer some diagnostic questions to select a diagnostic direction.
 Does the problem appear to be a leaking solenoid seal?
 Can be code be caused by a restriction in a valve or canister?
 Does the problem appear to be an electrical problem?
 Can you get a diagnostic direction from the diagnostic trouble codes?
 Some codes such as; Solenoid performance problem, have little detail.
Flow meter Testing
We use flow tester because they have measurable results for our before and after repair testing.
Notice the calibration setting on the right, these settings show calibrate flow rates that are used to set the red sliders on the flow gauge.
The photos show the difference in flow volume for 0.040” and 0.020” leaks.
Notice the big difference in the two flow rates where the red slider is set for a 0.040”
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calibration.
Full Flow and No Flow Indications
The full flow indicates verifies that the Evap system has no restrictions. The no flow indication verifies that the Evap system has no leaks. We use these two test for our after repair verification that the problem was corrected.
Purge Solenoid Resistance
Resistance test is frequently used for electrical testing. Limitation; it only checks the solenoid coil windings and not mechanical operation.
You need good resistance specifications and you need to check at room temeptature.
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Purge Solenoid Current Testing
Low amps probes can provide current values on a voltmeter or lab scope. Normal current flow indicates the complete circuit is normal. Neither test verifies solenoid mechanical performance but the current test verifies the electrical circuit plus the solenoid windings.
This example with 34Ω resistance has a current specification of 320 mA to 360 mA which indicates B+, ground and solenoid resistance are all normal.
The mechanical performance can be judged by blocking and passing vacuum for a handheld vacuum pump. You may want to floe test the open state to insure there is no restriction that may be overlooked with a vacuum pump.
OBDII Purge Valve Codes
• P0443 Purge Control Valve Circuit problem
• P0444 Purge Control Valve Circuit Open
• P0445 Purge Control Valve Circuit Shorted
• P0458 Purge Control Valve Circuit Low
• P0459 Purge Control Valve Circuit High
• P0496 Purge Control Valve Circuit Open
• P0497 Low purge vacuum when purge valve is open.
No single vehicle will have all these codes available.
P0443 Diagnostics
The code description “Evaporative Emission Control System Purge Control Valve Circuit” does not give a clear diagnostic direction. The keyword is circuit, indicating an electrical problem.
The PCM monitors the voltage status on the control circuit with the comprehensive component monitor that runs continuously. This diagnostic will apply to most vehicles.
Start with a baseline for full flow and blocked conditions to verify Evap system condition.
Seal and unseal the system to get a baseline before repair and repeat the test after a repair to verify improvement.
The code description indicates a circuit problem, so electrical testing is the best pin point test.
Use a vehicle specific diagram.
• An improper voltage level has been detected on the output circuit which controls the EVAP Canister Purge Solenoid Valve.
See next page for a full page diagram.
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Perform a voltage test at the PCM.
• Use bi-directional scan tool control to increase purge duty cycle.
• Voltage should be B+ with 0% duty cycle; voltage should decrease as duty cycle is increased.
If the voltage is missing,
Check for missing B+, open circuit in the wiring, open solenoid and poor connections in the purge solenoid circuit.
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Current Testing Code P0443
If the low amps probe indicates no current flow, check the B+ supply, solenoid resistance and PCM driver operation.
• Voltage should be B+ with 0% duty cycle; voltage should decrease as duty cycle is increased.
Current flow can be tested on the B+ circuit or control side of the solenoid circuit.
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Multimeter Amp Testing P0443
A multimeter amp test can be used to test the solenoid circuit.
• Test current flow with key on engine off.
• Move red lead to amps position.
The amp shunt is a fused circuit, move the lead back to volts when testing is complete.
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Current flow will be normal, if the solenoid is off and the circuit has B+ with normal solenoid resistance.
Remember, this test will not work, if the PCM driver or control circuit is shorted.
Current flow indications;
Solenoid resistance is 33 Ω with 12.6 V B+. That gives us 381.8 mA of current flow. Current flow should be near 400 mA.
If B+ is the problem, use a vehicle specific diagram to check fuses and connectors that supply B+ to the solenoid
. Ground is not tested with the multimeter test, it will be necessary to check the PCM and PCM grounds if the multimeter passed and the solenoid will not energize.
P0443 Diagnostics Resistance
Resistance test is used to verify solenoid winding resistance.
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P0443 Diagnostic Summary
The code was set because the voltage was not low with the solenoid energized or was not B+ with the solenoid off. Low amp probe testing is quick and does not require opening the circuit. The low amp probe can quickly identify a short to ground or shorted PCM driver. Resistance testing has a place in the diagnostic but it may not be the most efficient test early in the diagnostic process. Our approach is to use current flow to get a quick diagnostic direction to narrow down the areas to be tested and the check B+ and PCM control circuits.
P0444 Code Diagnostic
The code indicates the purge control circuit is open. The likely causes are missing B+ for the power side of the solenoid, Open solenoid. Open in the purge circuit or connector. This code is set by the comprehensive component monitor that runs continuously.
Check B+ to the purge solenoid
Use a vehicle specific diagram.
• B+ missing at control circuit for the Purge Solenoid Valve.
• Verify B+ at the control side of the solenoid.
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Check for B+ supply to the solenoid
• If it is missing, check the fuse and wiring for B+.
Purge P0445 Current flow Test
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The low amps probe should indicate zero amps with the solenoid off. Current flow with 0% duty cycle indicates a short circuit. If current flow is excessive with the solenoid energized a shorted solenoid is likely.
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Purge P0445 Resistance Test
Resistance test is used to check the solenoid winding resistance. If resistance is normal, check for a short to ground of shorted PCM driver.
P0445 Diagnostic Summary
The code is caused by higher than normal current flow.
Solenoid resistance is a likely cause. The PCM driver could be shorted. But this is a chance of shorted control circuit wiring shorted to B+.
P0458 Code Diagnostic
The code indicates a low voltage condition at the purge control circuit at the PCM with the solenoid de-energized. The code indicates a low voltage condition at the purge control circuit at the PCM with the solenoid de-energized.
This code can be set by a shorted PCM driver.
The code is set by the comprehensive component monitor.
There should be B+ at the PCM driver output with the solenoid off.
The most like cause is a short to ground in the solenoid control circuit.
This will cause continuous purge circuit current flow.
P0458 Code Current Diagnostic
Use a low amp probe to test if the PCM connector is not easily accessible. Current flow with zero duty cycle indicates a shorted control circuit or PCM driver Current flow can be tested on the B+ circuit or control circuit.
If the problem is intermittent, check current flow while the wiring harness and connectors are moved to try to duplicate the condition.
P0458 Diagnostic Summary
The code indicates the purge control circuit voltage at the output of the PCM driver stays high when the solenoid is energized.
There is a possibility of a shot to B+ in the control
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circuit.
Check the voltage at the purge control solenoid; it should drop as duty cycle is increased with bi-directional control with the scan tool.
P0459 Code Diagnostic
The code indicates the purge control circuit voltage at the output of the PCM driver stays high when the solenoid is energized. There is a possibility of a shot to B+ in the control circuit. Check the voltage at the purge control solenoid; it should drop as duty cycle is increased with bi-directional control with the scan tool. Check voltage when duty cycle is increased with bi-directional testing with a scan tool. If the voltage goes down as duty cycle is increased and gets below 1 V with 100% duty cycle, the problem is intermittent.
Check for intermittent B+ circuit if the code cannot be verify with resistance and voltage tests.
If the problem is intermittent, move the wiring harness and connector to check for intermittent conditions.
P0496 Code Diagnostics
The PCM detected purge flow when the purge was de-energized.
This is a non-continuous monitor that requires enabling conditions to run and stores data in mode 6.
A likely cause is a short to ground in the control circuit or a stuck open purge solenoid.
P0496 Current flow test
Use a low amp probe to test if the PCM connector is not easily accessible. Current flow with zero duty cycle indicates a shorted control circuit or PCM driver.
Current flow is present with the solenoid off, check the PCM drive and for a short to ground in the solenoid control circuit.
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P0496 Diagnostic Summary
The most likely cause is a shorted control circuit between the PCM and the solenoid.
The low voltage condition must last for 5 seconds to set the code or happen on a frequent basis.
If the wiring is not shorted, the PCM driver is the likely cause. Current flow is the best way to locate intermittent problem that sometimes happen with the code.
Purge Diagnostics Conclusion
The purge valve is common to most Evap system with some variation in the control circuits. The next area that is common to all Evap systems are the hoses. Hoses are the most likely area to cause a leak.
Evap Hoses
The hoses must connect the Evap system components the purge solenoid.
The purge flow sensor requires the hoses to operate. Leak checking is the only way to locate leaking hoses. But be sure the purge flow sensor on OBDI is not the causing a false leak code.
Evap Vacuum Switch
Check Evap vacuum switch before doing a leak check.
Apply a slight vacuum to close the switch, replace the vacuum switch, if it does not operate correctly.
A bad Evap vacuum switch can give a false leak code.
Evap Vacuum Switch Testing
The Evap vacuum switch applies B+ to the PCM input with no vacuum present. Disconnect the Evap vacuum switch and apply a slight vacuum, the voltage should drop to less than a volt.
Replace Evap vacuum switch replace the switch that fails this test.
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Evap Leak Codes
We are going to treat leak codes with a single set of procedures, even though the 0.020” leak (small leak) is more difficult to locate.
 P0440- Incorrect purge, possible leak
 P0442- Small leak detected
 P0455- Gross leak detected
 P0456- Small leak detected
 P0457- leak detected, possible filler cap loose/missing
We will use an OBDI leak check and an OBDII leak check because we have a vent seal valve on most OBDII systems.
Testing for leaks OBDI
Fuel Vapor lines are tested with a smoke machine, if there is no vent sealing solenoid so hoses will need to be block off to seal the system. Select a test point to seal a hose and perform a flow test with a flow meter.
Testing for leaks using the EVAP Test Port
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Connecting a Smoke Machine
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Select a Point to Test
Select a hose to pinch that will divide the system in half.
This point will check the hose between the purge solenoid and the canister.
Testing after the canister will require the canister to be seal with plastic wrap and rubber bands.
This may not be the easiest way to test, if it is difficult, disconnect the hose from the canister and check back to the flow sensor.
OBDI does not test he fuel tank or gas cap.
OBDII with a Vent Seal Solenoid
The addition of a vent seal solenoid allows technicians to seal the system with bi-directional control with a scan tool. Chrysler vehicle use alternative approaches that don not use an electrical seal solenoid. The differences will be covered separately with the unique testing required for those systems. The first issue is leak testing with bi-directional control with a scan tool.
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Typical Vent Seal Application
Most Evap systems capable of detecting a 0.020” leak use a vent seal solenoid. Chrysler vehicles are an exception.
Check the smoke machine for full flow and no flow conditions. We are also going to use the 0.02” leak calibration.
Restrictions will prevent the ball from reaching the top of the gauge. No flow conditions will have the ball at the bottom of the gauge.
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Sealing the system with the vent solenoid
Most OBDII Evap systems have a vent seal solenoid to seal the system for the 0.02” leak test.
Bi-directional control with a scan tool
Select the Evaporative Emissions Canister Vent to activate.
Then select the off position to turn the vent on or closed.
We can use a service bay Evap test on most new vehicles that use a vent solenoid.
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Service Bay Evap Test
The scan tool shows the progress of the test and the test results. This is the 0.040” leak test. A 0.020” leak will require a smoke machine.
If a vent seal is not available, seal off hoses like we did for OBDI.
We can activate manually if a vent seal when bi-directional operation is not possible.
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Vent Seal Solenoid Circuit
We can calibrate the flow meter for 0.040” and 0.02” leaks.
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Calibrating the Flow Gauge for Leaks
The red slider is moved to the location selected to mark the leak calibration.
The 0.040” calibration is selected currently.
If you discover a leak, you can divide the system by blocking hoses as we have done in the past.
The smoke is used when you have identified an area with the leak.
You may want to separate the tank and gas cap from the canister as point to divide the system. Find a location that is accessible and understand the area being tested.
Use the calibration to determine the size of the leak.
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Use the Smoke
By narrowing the area it is easier to locate the smoke.
Many smoke machines have a UV dye that can help identify leaks where it is difficult to see the smoke.
The UV dye helped identify the joint as the leak.
Sometimes locations are difficult ti identify with just smoke, like the seal on the top of the gas tank.
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Purge with a Vent Open
The vent seal solenoid is off in a normally open position during normal purge. We test for restrictions when the vent ids open.
Normal Evap systems have little restriction.
A restriction will create a vacuum during purge that will change the fuel tank pressure sensor readings.
Vent Seal Solenoid Codes
 P0446- Evap vent seal solenoid malfunction
 P0447- Evap vent seal solenoid control circuit open
 P0448- Evap vent seal solenoid control circuit shorted to B+
 P0449- Evap vent seal solenoid malfunction, sometimes the result of a restriction in the canister or vent seal solenoid.
 P0498- Evap vent seal solenoid control circuit low
 P0499- Evap vent seal solenoid control circuit high
Chrysler codes have different meanings, see the system specific section.
Remember, no single vehicle will have all these codes.
We will use bi-directional control on a scan tool for our initial testing.
Use a combination of the testing with a scan tool and flow meter to find the way that works best for you.
We recommend using flow meters to verify vent operation.
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Code P0446
The vent seal solenoid control signal voltage did not match the solenoid command. This code is set by the comprehensive component monitor.
100% duty cycle voltage should be less than 4 volts and usually under 1 volt.
0% duty cycle should be near B+
Use a voltmeter to monitor control signal voltage with varying vent seal solenoid duty cycle.
Current flow can also be used if the voltage appears to be normal.
• Current flow with 0% cycle duty indicates a shorted control circuit or PCM driver.
• 100% duty cycle
should have typical current flow.
If current does not respond with normal current flow, check the wiring and solenoid resistance.
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Code P0447
Evap vent seal solenoid control circuit was low when the vent seal control was de-energized.
The PCM detected the wrong control signal voltage.
0% duty cycle control signal voltage should be near B+
This code is set by the comprehensive component monitor.
Check for open control circuit, short to ground in the control circuit or a shorted PCM output driver. Some manufacturers use this code for slow vacuum decay after the vent seal is opened. Low flow meter readings indicate a restriction in the Evap system between the test port and the vent exhaust
We are going to use voltage to check circuit operation.
Use a low amp probe to test if the PCM connector is not easily accessible.
Current flow with zero duty cycle indicates a shorted control circuit or PCM driver.
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Low Amp testing
Current flow checks the complete circuit including solenoid resistance and is a good check to verify repairs.
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Code P0447 Summary
Use a combination of the testing offered to find the way that works best with your equipment. Current testing is better than solenoid resistance testing. Current checks the complete circuit including PCM ground.
Code P0448
The vent solenoid control circuit is shorted to B+. Check the control circuit with a voltmeter. Use a combination of the testing offered to find the way that works best with your equipment. Current testing is better than solenoid resistance testing. Current checks the complete circuit including PCM ground. Use a voltmeter to check the vent control; circuit.
• Current flow with 0% cycle duty indicates a shorted control circuit or PCM driver.
• 100% duty cycle should have typical current flow.
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Code P0449
Evap vent seal solenoid malfunction, sometimes the result of a restriction in the canister or vent seal solenoid.
Use a flow meter to check for normal flow with the vent open and closed, you can verify the vent in scan data.
The control circuit may be open causing control voltage to be high.
Use a combination of the testing offered to find the way that works best with your equipment. We recommend using flow meters to verify vent operation.
The flow meter should show full flow with the vent solenoid de-energized.
Scan data can be use with the fuel tank pressure sensor that is usually used when a vent solenoid is used. Fuel tank pressure shuld not have large voltage changes when purge is started.
This a GM example. The fuel tank pressure sensor voltage changes about 0.02 volts when purge is started. This small change indicates a low restriction which is what is expected.
The code is not clear about the exact cause of the malfunction so voltage checks should also be done.
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Voltage should be battery volts with vent de-energized and under 1 volt with valve energized.
Restricted Vent Solenoid
This filter is from a farm truck that operated in a dirty environment.
This truck’s fuel tank pressure sensor voltage had major voltage changes when purge started.
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Code P0498
Evap vent seal solenoid control circuit was low when the vent seal control was de-energized.
The PCM detected the wrong control signal voltage.
0% duty cycle control signal voltage should be near B+
This code is set by the comprehensive component monitor.
Check for open control circuit, short to ground in the control circuit or a shorted PCM output driver.
Some manufacturers use this code for slow vacuum decay after the vent seal is opened. Low flow meter indications indicate a restriction.
We will start with voltage testing the vent control circuit. Voltage should be battery volts with no vent de-energized and less than 1 volt with valve energized.
Current flow testing
• Current flow with 0% cycle duty indicates a shorted control circuit or PCM driver.
• 100% duty cycle should have typical current flow.
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Code P0499
Evap vent seal solenoid malfunction, sometimes the result of a restriction in the canister or vent seal solenoid. Use a flow meter to check for normal flow with the vent open and closed, you can verify the vent in scan data. The control circuit may be open causing control voltage to be high.
This code must be check for an electrical problem and a flow restriction.
Code P0499 Flow Restriction Test
0% duty cycle for full flow should and should low restriction.
During testing monitor vent flow while energizing and de-energizing the vent solenoid.
Flow should respond quickly and go from full flow with the solenoid de-energized to no flow with the solenoid energized.
Code P0499 Voltage Test
Voltage should be battery volts with vent solenoid energized and less than 1 volt with vent solenoid energized.
Code P0499 Summary
The vent solenoid must respond to the PCM command to have proper flow control. Verify flow and control signal voltage.
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Fuel Tank Pressure Sensor Codes
Accurate fuel tank pressure is critical to the leak test and to control the fuel tank vacuum. There have been cases where an out of calibration fuel tank pressure sensor has caused fuel tank failures.
 P0450 fuel tank pressure sensor malfunction.
 P0451 fuel tank pressure sensor signal does not appear to show normal signal changes during purge operation.
 P0452 fuel tank pressure sensor signal below normal range.
 P0453 fuel tank pressure sensor signal above normal range.
 P0454 fuel tank pressure sensor signal intermittent.
FTP Code Diagnostics
We are going to diagnose FTP codes as a group since the test procedures are redundant. Compare key on engine off values to typical readings for the vehicle being tested.
Signal voltage testing is done by the comprehensive component monitor typical values;
Typical GM 1.3 to 1.7 volts
Typical Ford 2.5 to 2.7 volts
Typical Nissan near 1.8 volts
Typical Hyundai -2 mm HG to 2 mm HG
FTP Sensor Voltage Test
The second part of the test is the sensor response to urge operation.
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GM Scan Data Recording
The graph of this GM vehicle shows typical FTP signal activity during a test drive.
Fuel tank pressure changes little when purge is started which indicates normal operation for the voltage and flow restriction test.
Test drive recording like this can detect most of the code problems with a fuel tank pressure sensor and then pin pointed with a voltage test.
Now it is time to look at the specific manufacturer strategies.
System Specific Operation
We are going to cover the most widely used versions of enhanced Evap monitors. Mode 6 will be used to help with advanced diagnostics for Evap. Mode 6 data support by some scan tools are not as user friendly as they could be and may require extra effort but the data is worth the extra effort. Manufacturers are not required to make their information easy to understand, they are required to make Mode 6 available. Mode 6 was designed and written by engineers.
Evap Pressure Vacuum Decay
Vacuum decay is widely used in the 2000 to 2004 time frame. Some natural vacuum systems use the same components with software improvements. Vacuum decay is widely used by import and domestic vehicles.
The main drawback is a 4 to 6 hour wait after engine shut down before the monitor will run.
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Vacuum Decay Leak testing
The vent seal solenoid seals the outlet for the canister to test for leaks. The purge valve opens to build a vacuum while the vent solenoid is energized to capture a vacuum in the Evap system.
Evap Monitor Vacuum
The Evap monitor is a series of test for vacuum at different points of the test.
This example is a GM Fuel tank Pressure voltage graph.
The dashed lines represent points where the PCm records data during the test sequence. The data values are stored in Mode 6.
Some of the data points are done to record a specifc signal value for evaluation in a later test.
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First Phase of Vacuum decau test
The purge and vent solenoids are closed.
Monitor tank pressure with vent and purge closed. The test results are stored in mode 6 as purge valve test results. GM Fuel tank Pressure voltage is used in this example.
The PCM watches for vacuum increase with both solenoids closed. Purge valve leakage will allow a vacuum to build with the purge valve closed. Warm fuel and rough road conditions will cause a slight increase in fuel tank pressure.
Mode 6 for Purge monitor
GM mode 6 monitor 3D test ID C4 stores the test result rise in pressure with purge and vent valves closed.
Monitor 3D test ID C5 monitors vacuum rise with purge and vent valves closed.
Mode 6 for Honda Purge monitor
The difference in manufacture information can make Mode 6 data difficult to understand. This is the mode 6 purge monitor information for Honda. Remember, the two manufacturers are doing the same test with their unique way of showing the test criteria.
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Mode 6 Data Analysis
Each manufacturer has their unique Monitor ID and Test ID numbers.
Some scan tools give good definitions of MIDs and TIDs.
This example of Mode 6 scan data is from Ford. Ford fully supports Mode 6 diagnostics in their scan data information. Monitor 3D Test ID 82 is the specification and test result for vacuum blocking test. All zeroes indicate the monitor has not run since the battery was reconnected on this new police car just out of the paint shop. The data explanations are excellent, just remember, scan data is the actual results of the monitor test that ran last. This example indicates the monitor has not run since the codes were cleared.
Mode 6 Specifications
Mode 6 data provides the max and min specifications were they apply and the test results of the monitor testing.
The strength of Mode 6 is that the monitor testing is performed under PCM controlled conditions, which makes them accurate. The monitor test results are used to turn on the MIL for trouble codes.
The sampling of data shows you the differences in how manufacturers define their Mode 6 data. We will use the Ford IDS for instructional purposes since it provides good descriptions. Don’t assume all scan tools display this much information on the screen.
Second Phase of Evap Test
The vacuum built test tries to build a 6 to 9 IN H2O vacuum in the Evap system. This target will not be possible if there is a gross leak in the system. This test is referred to as the weak vacuum test. The PCM uses recent re-fueling events to trigger gas cap alerts when the monitor fails.
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Vent sealed the system and purge is duty cycled to build a vacuum.
Vacuum can go quickly if the purge hoses are blocked or kinked.
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Blocked Purge Hose Test
The speed of the vacuum build up can indicate a blocked purge hose and is part of the second phase test. A blocked hose can cause a high vacuum reading because of the small area to be evacuated.
In this example we have three test results stored for one phase of the test.
Mode 6 Weak Vacuum Test
Ford’s IDS mode 6 test results for the weak vacuum test. If the system cannot reach the 6 to 9 IN H2O range it indicates a gross leak. Mode 6 data will show the max and min limits for the three test IDs.
Use this data during your initial diagnostic;
Remember, it may be difficult to get this test to run if the vehicle is not shut down for 4 to 6 hours; it will be difficult to use this data for verification of a repair.
Third Phase of Evap Test
The vacuum readings are allowed to stabilize before starting the timed vacuum decay test Seal the Evap system and allow readings to stabilize. A large leak will allow the vacuum to escape before the decay test is started.
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Fourth Phase of Evap Test
The timed 0.020” and 0.040” vacuum decay test is started because the vacuum held long enough to pass the large leak test.
The 0.040” leak test passes with a higher vacuum decay rate than the 0.020” leak test.
Fifth Phase of Evap Test
The 2nd vacuum reading is the final leak check reading, if the decay is below the 0.020” calculated value, the leak check is complete.
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Sixth Phase of Evap Test
The vent is opened and the decay rate of the vacuum is used to check for restrictions in the canister and vent seal solenoid. This is a second restriction test; the first was a kinked purge hose
Natural Vacuum Evap Test
Natural vacuum leak check uses the same components as vacuum decay. Natural vacuum is done after engine shut down and does not require a 4 to 6 hour wait after engine shut down to operate like vacuum decay. Test runs after engine shut down, which may take 45 minutes to complete. We will use Ford as an example, all engine off natural vacuum will have similar operation but the Ford Mode 6 scan data is a good for instructional purposes.
Engine off Natural Vacuum
Natural vacuum uses the expansion of warm fuel and contraction of cool fuel to create positive and negative (vacuum) pressure. The natural vacuum test is done to detect 0.020” leaks; the 0.040” leak test is done at cruising speed with vacuum decay method. The 0.040” leak check can be done with a scan tool in the service bay.
Ford’s EONV Phase 0
Phase 0- Fuel tank pressure is allowed to stabilize for 2 minutes after shut down with the vent seal valve open (de-energized). Fuel has been heated by driving the vehicle which will cause the fuel to vaporize after shut down generating pressure and then contract as it cools down creating a natural vacuum. Ford tests both the pressure rise and the natural vacuum that results from cooling fuel.
Ford’s EONV Phase 1
Phase 1 starts when the vent is closed after the stabilization is complete. The PCM monitors the pressure build to see if it meets a calibrated threshold for pressure. The pressure threshold is determined by fuel level and ambient temperature, the specifications used will be in Mode 6 data for the last time the monitor ran. If the pressure threshold is reached, the test passed and the monitor goes to test phase 4 to record a passed test result.
If the fuel tank pressure reaches a plateau without reaching the pressure threshold, the monitor goes to test
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phase 2.
Ford’s EONV Phase 2
Phase 2 only runs if the pressure threshold was not reached during test phase 1. The vent is opened to zero the tank pressure with a 2 minute stabilization period. The fuel tank pressure value is stored and the monitor goes to test phase 3. Next we will look at the pressure/vacuum data of this process.
Engine off Natural Vacuum Graph
Warm fuel will cause the tank pressure to increase with the vent closed to seal the Evap system.
Ford’s EONV Phase 3
Phase 3 only runs if the pressure threshold was not reached in test phase 1. Phase 2 re-zeroed tank pressure after a pressure increase after shut down. The vent is closed to seal the Evap system on fuel that has expanded, which will cause a vacuum to result. Phase 3 will last for a maximum of 45 minutes after leaving phase 2 unless the vacuum threshold is reached indicating no leak. If the test reaches the vacuum threshold, the monitor goes to test phase 4 to record a passed test. Phase three only runs if the heat in the fuel was too low to create enough pressure to pass phase 2, so vacuum may not reach the vacuum threshold. Phase 3 averages four failed attempts to create a vacuum before recording a failure and go to test phase 4 to record a failed test. It can take 8 failures of test phase 3 to turn on the check engine lamp, if the failure only shows up in test phase 3.
Test phase 3 passes when the vacuum build up reaches the threshold that is determined by ambient temperature. The threshold values will be displayed in Mode 6.
Ford EONV Mode 6
Mode 6 Monitor ID 3C is data for the 0.020” leak test.
Test ID 81 displays the test result for the pressure threshold.
Teat ID 82 displays the test result for the vacuum test.
Test ID 83 is the fault counter for aborted test that did not reach the pressure and vacuum thresholds.
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Ford’s EONV Phase 4
Phase 4 stored the test results in mode 6 to manage the check engine light and record the test results for the test phases.
GM Engine off Natural Vacuum
Other vehicle manufacturers use natural vacuum but their test descriptions may not be as clear as Ford’s. The data can still be used even if the test descriptions are not as clear as Ford’s descriptions.
GM Mode 6 as an example;
Chrysler Evap Systems
Chrysler uses unique Evap leak detection systems;
Leak Detection Pump-LDP
Natural Vacuum Leak Detection- NVLD
Evap System integrity monitor- ESIM
Chrysler Leak Detection Pump
Engine vacuum is used to pull up a spring loaded diaphragm when a vacuum switching valve is opened. The diaphragm is released creating pumping action to use pressure for leak testing. The vent valve is sealed when the diaphragm is closed by the spring which pressurizes the Evap system. After a number of cycles, the pressure holds the diaphragm open when pressure reaches 3 to 6’ H2O.
LDP in Purge Mode
The control valve blocks manifold vacuum to the diaphragm and allows ambient air pressure into the diaphragm chamber.
The vent valve in the bottom is open for normal purge.
The reed switch that indicates the up position of the diaphragm is un-grounded. The switch signal is B+ when the switch is open.
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LDP Vacuum Applied
Vacuum pulls the diaphragm up when the control valve is opened. The reed switch closes indicating the diaphragm is in the up position. The PCM closes the control valve to allow the spring to push the diaphragm down to compress the air in the chamber.
This cycle repeat until 3 to 6 “H2O of pressure in the Evap system holds the diaphragm up.
The PCM times the time the reed switch is held open by the pressure to test for leaks
Chrysler uses leak checks for; gross leaks. 0.090” leaks and 0.020’” leaks.
LDP Self-Test
The Leak Detection Pump can be tested with a service bay test on some scan tools.
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LDP Lab Scope Testing
A lab scope can be used to display the duty cycle of the control valve stops after the reed switch stays closed and a timer starts to check for pressure drop off which is indicated by the switch closing.
Normal LDP Duty Cycle Signal
The left control valve duty cycle pattern is the start of the LDP pumping action. The duty cycle stops when the reed switch remains at ground indicating the switch is closed.
The PCM times the time it takes for the reed switch to open again as pressure decreases.
Large Leak Duty Cycle Pattern
The reed switch does not stay closed when there is a large leak. An advantage of the LDP is that it can identify a 0.020” leak in the service bay. The reed switch does not remain closed when a large leak is present.
Leak Detection Pump Mode 6
Mode 6 data is a short list that covers 0.040”. 0.02” leak and pinched purge line to the leak detection pump.
The descriptions give us a good diagnostic direction. The enabling conditions can store mode 6 for long periods before they are replaced when a monitor finally runs.
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Chrysler Natural Vacuum Leak Detection
NVLD has four active components;
 A large diaphragm opens at a pressure of 0.5” H2O for re-fuelling and pressure relief.
 An electric solenoid that opens for normal purge.
 A small diaphragm that opens at 3 to 6” H2O to limit vacuum.
 A vacuum switch that closes near 1” H2O to indicate engine off vacuum for the leak test.
Chrysler NVLD Operation
NVLD checks for small leaks after engine shut down.
The pressure relief limits pressure build up to 0.5” H2O. Cooling fuel creates a natural vacuum. 3⁰ F Temperatures in fuel temperature produces about 1” H2O vacuum. The PCM measures the time until the vacuum switch closes after engine shut down. The PCM ignores the switch the first 10 minutes and does not start accumulating engine off time until the first 60 minutes have passed. The PCM will accumulate the engine off time until 4,200 minutes are accumulated without a vacuum switch closure and there must be a total of 100 minutes of engine run time to set a failure. The PCM will run the timer up to 17.5 hours after shut down.
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Chrysler NVLD Mode 6
There are four Mode 6 Monitor IDs for NVLD.
Monitor 3C runs with the engine off while MID 39, 3A. And 3D is run with the engine running.
Chrysler ESIM
Chrysler replaced their NVLD module with the Evaporative System Integrity Module in 2007.
The ESIM module is a mechanical method of measuring small vacuum levels The ESIM has a vacuum actuated switch that closes when a 0.8 to 2.2 “H2O vacuum is present at the inlet to the canister. Remember, the sealing force is gravity, the weight of the check valve keeps it closed, and there are no springs to close the check valve. The angle of the canister and ESIM module is critical.
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ESIM Action
Two check valves use gravity to seal the inlet to the canister, a 0.8 to 2.2 “H2O vacuum closes the vacuum switch which operates with the engine off by natural vacuum. A pressure check valve opens at 0.5 “H2O to permit re-fuelling.
The vacuum check valve opens at 0.8 to 2.2 “H2O vacuum which causes the closes the vacuum switch to close indicating a natural vacuum has formed and the test is complete. The large check valve is for pressure, the small check valve is for vacuum and the vacuum diaphragm closes the switch.
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ESIM Pressure Relief
0.5 “H2O Pressure in the fuel tank lifts the large check valve off its seat to allow vapor to enter the canister during re-fueling operation and pressure relief after engine shutdown.
Natural Vacuum Action
The first stage of natural vacuum is to allow the pressure to vent into the canister when the fuel is hot.
The pressure relief check valve will open at 0.5”H2O Pressure, which makes a natural vacuum easier to develop.
Developing a Vacuum
Fuel that is cooling will drop the pressure below 0.5”H2O and the pressure check valve will close sealing the inlet to the canister.
The fuel volume shrinks as the fuel cools which creates a natural vacuum. A weak 0.8 to 2.2 “H2O vacuum will
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develop as the fuel cools, if there are no leaks in the Evap system. A 3 ⁰ F temperature drop will create about 1 “H2O of vacuum. This may take as long as 4 hours. Hot fuel creates a natural vacuum faster than cold fuel.
The enabling criteria include vehicle operation for at least 10 minutes with vehicle in motion to heat the fuel.
Chrysler ESIM Diagram
ESIM input circuit. The vacuum switch will close when vacuum drops to 0.8 to 2.2”H2O.
Model Specific Application
There are four calibrations of the ASIM. Notice there are only two pins in the connectors.
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ESIM Natural Vacuum Results
The PCM monitors the time it takes to create a 0.5 to 2.2 “H2O vacuum to close the vacuum switch. PCM software accumulates the time and determines a pass/fail based on driving time for heating the fuel and ambient temperature for cooling. It may take as many as 10 consecutive failed attempts at developing a natural vacuum to set a code with short trips. During normal purge operation the PCM observes the vacuum switch closing as a check for a gross leak.
Toyota non-Intrusive Evap
Toyota non-intrusive Evap systems were used from 1996-2000.
This system can test the canister and the fuel tank separately. The system does not use a vent close valve on this version of Evap.
Toyota Air Drain Valve
The air drain valve is a pressure relief valve that opens at approximately 0.40 psi.
Toyota Air inlet Valve
The air inlet valve opens when purge vacuum is applied.
Toyota Vapor Switching Valve
The vapor switching valve selects the canister section for vacuum decay testing when it is de-energized. The vapor switching valve opens to select the fuel tank for vacuum decay test. The PCM monitors the pressure change when the valve is energized to open the tank side of the Evap system.
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Non-Intrusive System Testing
Leak testing requires that air drain valve hose be blocked to leak check a Toyota non-intrusive Evap systems.
Toyota Intrusive Evap
Many of the components are similar to the non-intrusive system with the addition of a bypass valve and a vent seal valve.
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Toyota Bypass Valve
The bypass valve is in the de-energize state to perform the vacuum decay of the fuel tank. The bypass is energized to perform the vacuum decay test of the complete Evap system.
The air drain and air inlet vale operate like they do on the non-intrusive system. The vent seal or canister close solenoid is used to seal the system for vacuum decay testing similar to what was covered earlier.
Toyota Key off Evap Test
Toyota’s Key off Evap monitor has an electric pump that runs after the engine has been off for 5 hours. Coolant temperature must be under 95⁰ F after 5 hours for the monitor to run; if the temperature is not under 95⁰ F the timer has two 2 hour extensions during hot conditions.
An engine running Evap test is also run by opening the purge valve and monitoring fuel tank pressure for a small change in vacuum (3.75 mmHg) indicating normal Evap purge.
If the pressure change is too small the purge monitor fails. The ECM sets a two trip code for the purge valve operation (P0441). The vent seal valve is located inside the pump assembly.
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Key off Evap Timing Chart
Operation in the A region;
The ECM stored atmospheric pressure values fuel tank pressure voltage should be about 3.67 V.
Operation in the B region;
The ECM monitors the vacuum levels when the calibrated 0.020” orifice is connected to the pump output with the vent and purge valve closed.
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Operation in the C region;
The ECM monitors the vacuum levels with the vent seal valve closed and determines the rate of leakage.
Operation in the D region;
The ECM monitors the vacuum levels when the purge valve is opened with the vent closed. The vacuum level drops quickly if there are no restrictions in the system.
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Operation in the E region;
The ECM monitors the vacuum levels when the calibrated 0.020” orifice is connected to the pump output with the vent and purge valve closed.
DM-TL Evap System for Imports
The system has an electric pump the works similar to the Toyota system with some key differences.
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DM-TL Evap System Orifices
The system has two calibrated orifices.
The small orifice is 0.50 mm with a larger 1.0 mm orifice to detect two levels of leaks.
DM-TL Evap System Test
The system measures the amperage draw of the electric motor for the pump to judge the rate of leakage. A large leak will have a very low amp draw while a small leak will be closer to the amp draw of the calibrated orifice.
DM-TL Pressure/Current Chart
The chart show current values for three conditions
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Evap Diagnostic Summary
It is our hope that you have a good understanding of Evaporative Emission monitors and the differences that exist. I will be happy to help with any Evap problems you encounter. This program is a joint venture with the school to improve your diagnostic skills.