Chart C-3 Evaporative Emission Control System

Chart C-3:

EVAP Solenoid Circuit:

CIRCUIT DESCRIPTION:
Canister purge is controlled by a solenoid that allows manifold vacuum to purge the EVAP canister when de energized. The ECM supplies a ground to energize the solenoid (purge "OFF"). The EVAP purge solenoid controlled by the ECM is pulse width modulated (turned "ON" and "OFF" several times a second). The duty cycle (pulse width) is determined by the amount of air flow, and the engine vacuum as determined by the MAP sensor input.

The duty cycle is calculated by the ECM and the output commanded when the following conditions have been met:

^ Engine run time after start more than 3 minutes.
^ Coolant temperature above 80°C.
^ Vehicle speed above 15 mph.
^ Throttle "OFF" idle.

Also, if the diagnostic "test" terminal is grounded, with the engine stopped, the EVAP purge solenoid is deenergized (purge "ON").

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

1. Checks to see if the solenoid is opened or closed. The solenoid is normally energized in this step; so it should be closed.

2. Checks for a complete circuit. Normally, there is ignition voltage on CKT 39 and the ECM provides a ground on CKT 428.

3. Completes functional check by grounding "test" terminal. This should normally de-energize the solenoid opening the valve which should allow the vacuum to drop (purge "ON").