Chart C-3 Evaporative Emission Control System

Chart C-3:

Chart C-3 Circuit:

CIRCUIT DESCRIPTION
Evaporation (EVAP) canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when energized. The Powertrain Control Module (PCM) supplies a ground to energize the solenoid (purge "ON"). The purge solenoid controlled by the PCM is Pulse Width Modulated (PWM) (turned "ON" and "OFF" several times a second). The duty cycle (pulse width) is determined by the amount of air flow and engine vacuum as determined by the Manifold Absolute Pressure (MAP) sensor input. The duty cycle is calculated by the PCM and the output commanded when the following conditions have been met:
^ Engine run time after start more than 3 minutes.
^ Engine Coolant Temperature (ECT) above 8O° C (176° F).
^ Vehicle speed above 13 mph.
^ Throttle at idle (about 3%).

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

1. This checks to see if the solenoid is opened or closed. The solenoid is normally de-energized in this step, so it should be closed.
2. Determines whether solenoid was open due to an electrical circuit problem or solenoid valve itself is faulty.
3. This completes a functional check by grounding the test terminal. This should normally energize the solenoid and allow the vacuum to drop (purge "ON").
4. Vacuum hose to manifold vacuum is either open or obstructed.

DIAGNOSTIC AIDS
Normal operation of the canister purge solenoid valve is described as follows:
^ Ignition "ON," engine "OFF," the evaporative purge solenoid valve should not be energized.
^ Ignition "ON," engine "OFF," tech 1 scan tool installed with "Output Tests" and "EVAP Purge" energized, the evaporative canister purge solenoid should be energized.
^ An inoperative evaporative cannister purge system can cause a rich oxygen sensor signal condition Diagnostic Trouble Code (DTC) 45. If the solenoid valve should become stuck open or the carbon canister become saturated, a continuous rich fuel condition may result.