Diagnostic Procedures

The following procedures are used to diagnose the Diagnostic Trouble Codes (DTC) listed above.

1. Check the purge control valve by blowing through the valve with the engine off. If any air passes through the valve, it is faulty. Replace the canister and purge control valve, be certain the lines in the system are free of debris, and retest the system to see if the purge valve operation is correct.

2. If no air passes through the valve, check the voltage at the DPS. A properly operating system should have about 2.4 to 2.8 volts at the DPS with the purge solenoid "off", and 1.5 to 2.5 volts with the purge solenoid "on".

3. If the voltage is very low, check the two way valve (small blue plastic valve at the canister) and make sure the arrow on the valve is pointing toward the CCV.

4. Check the vent lines and canister for restriction. You should be able to blow through the canister and CCV with the engine off. Be certain that all the lines in the system are free of debris and verify the integrity of the charcoal canister.





Above is an example of an HDS test showing normal evaporative emission control system operation at the 20 minute test interval.

1. At point "A" the purge control valve began operating, causing the tank pressure to begin to drop.

2. At point "B" the CCV closed.

3. The DPS voltage began to decrease at point "D" due to the drop of the tank pressure.

4. The PCM observed the DPS at point "C", where the canister purge stopped, to point "E", where the CCV opened. If the DPS voltage does not go up between point 'C' and point 'E', there is no leak and the test has been passed.





The above graphs are of the HDS test of a normal system operating with a high percentage purge control valve duty cycle. As the purge canister valve duty cycle increases, the DPS voltage decreases. Note the DPS voltage is 1.80 volts on the second graph, slightly lower than the 2.48 volts normally seen when the purge control valve is closed, as noted on the first graph.





Above is an example of abnormal evaporative system operation. DPS voltage is very low (0.56 volts) indicating a two way valve is installed backwards (the correct direction is with the arrow on the two way valve pointing toward the CCV), restricted canister, twisted or restricted canister filter or vent tube, or excessive purge control valve flow (possibly valve stuck open). A properly operating system should have about 2.4 to 2.8 volts at the DPS with the purge solenoid "off", and 1.5 to 2.5 volts with the purge solenoid "on".