Evaporative Emissions System: Testing and Inspection

Chart C-3:

Evaporative Emission Canister Purge Solenoid Wiring Schematic:

CIRCUIT DESCRIPTION
Evaporative Emission (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 "OFF"). The purge solenoid controlled by the PCM 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 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 above 8O°C (176°F).
^ Vehicle speed above 13 mph.
^ Throttle at idle (about 3%).

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


CHART 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 AID

The canister purge solenoid is a normally open solenoid valve. Normal operation is as follows:

^ Ignition "ON," engine "OFF," diagnostic test terminal of Data Link Connector (DLC) "NOT" grounded - purge solenoid should be energized (valve closed).
^ Ignition "ON", engine "OFF", diagnostic test terminal of DLC grounded - purge solenoid should "NOT" be energized (valve open).
^ An inoperative EVAP cannister purge system can cause a rich exhaust condition and may set a 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.