Evaporative Emissions System: Testing and Inspection

Purge Solenoid Circuit Diagram:

CIRCUIT DESCRIPTION:
The canister purge is controlled by a solenoid that allows vacuum to the fuel vapor canister when energized. The solenoid gets power when the ignition is turned "ON" and becomes energized when the PCM completes the circuit to ground.

Canister Purge Valve Check (Chart C-3):

CANISTER PURGE VALVE CHECK

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 closed (de-energized).
2. This step is used to determine if the solenoid has power and ground through the wiring (should have power from the ignition and be grounded through the PCM.)
3. This completes a functional check by grounding the test terminal. This should normally energize the solenoid and allow the vacuum to drop.

NOTE: Once the test sequence is completed, clear codes, operate vehicle, and check for recurring trouble codes.

DIAGNOSTIC AID

The canister purge solenoid is a normally closed solenoid valve. Normal operation is as follows:
1. Ignition "ON"; engine "OFF"; diagnostic test terminal of ALDL NOT grounded - purge solenoid should NOT be energized (valve closed).
2. Ignition "ON"; engine "OFF"; diagnostic test terminal of ALDL grounded - purge solenoid should be energized (valve open).
3. Engine running at normal operating temperature; engine has been running at least 3 minutes; vehicle speed greater than 13 mph; throttle valve open greater than 3% - purge solenoid energized (valve open).


Incorrect operation may cause the following:

1. Poor idle, stalling and poor driveability. Check for:

a. Inoperative or defective purge valve or solenoid
b. Damaged canister
c. Hoses split, cracked or not connected to the proper tubes
d. Pinched or plugged hose(s).

2. Evidence of fuel loss or fuel vapor odor. Check for:

a. Liquid fuel leaking from fuel lines, fuel pump, or injectors
b. Cracked or damaged canister
c. Inoperative canister control valve
d. Disconnected, misrouted, kinked, deteriorated or damaged vapor hoses, or control hoses
e. If the solenoid is always open, the canister may purge all the time. This can allow extra fuel at idle or during warm-up, which can cause a rough idle or a rich operation
f. If the solenoid is always closed, the canister can become over-loaded, resulting in fuel odor.

3. Continuous rich exhaust condition (trouble code 45). Check for:
a. Canister saturated with liquid fuel.
b. Purge solenoid stuck open.