Evaporative Emissions System: Testing and Inspection

Chart C-3:

Wiring Diagram for Canister Purge:

CIRCUIT DESCRIPTION:

The canister purge is controlled by a solenoid that allows ported vacuum to purge the canister when energized. The ECM controls the ground to activate the solenoid. If the following conditions exists, while the engine is running, the canister purge solenoid is energized (purge ON).

1. The engine run time is more than one minute.
2. The coolant temperature is above 80°C or 176°F.
3. The vehicle speed is above 5 mph.
4. The throttle is off-idle. TPS signal is approximately 0.75 volts.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This checks to see if the solenoid is opened or closed. It should be open (energized).

2. This completes the functional check by grounding the diagnostic test terminal. This should normally de-energized the purge solenoid and allow the vacuum to drop.

3. This checks for a complete circuit. Normally there is ignition voltage on circuit 39, and the ECM provides the ground path on circuit 428. A shorted purge solenoid could cause an open circuit in the ECM.


NOTE: Once the test sequence is completed, clear codes and verify NO "SERVICE ENGINE SOON" light exists.



DIAGNOSTIC AIDS:

This describes the normal operation of the canister purge solenoid.
With the ignition "ON," engine "OFF", and diagnostic test terminal not grounded, the canister purge solenoid will be energized. With the ignition "ON," engine off, and diagnostic test terminal grounded, the canister purge solenoid will be de-energized.