Evaporative Emissions System: Testing and Inspection

Chart C-3:

Evaporative Canister Wiring Diagram:

CIRCUIT DESCRIPTION:

The canister purge is controlled by a solenoid that allows ported vacuum to purge the fuel vapor canister when energized. The ECM controls the ground to power the solenoid. If the diagnostic test terminal is grounded, with the engine not running, or the following conditions exists while the engine is running, the purge solenoid is energized (purge "ON").

^ The engine run time is more than one minute.
^ The coolant temperature is above 75~C or 167~F.
^ The vehicle speed is above 15 mph.
^ The throttle is off-idle.



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

1. The external vacuum source must be applied to the canister purge solenoid at the canister.

2. Grounding the diagnostic test terminal will energize the canister purge solenoid and permit vacuum to pass.

3. Some canister purge solenoids may have a large bleed designed into the solenoid, and may appear to be operating incorrectly.


DIAGNOSTIC AIDS:

^ Inspect the canister for cracks or fuel saturation.

^ Inspect fuel vapor lines from the fuel tank for leaks, being disconnected or sharp bends blocking the flow of vapors.