Evaporative Emissions System: Testing and Inspection

Chart C-3:

Canister Purge Solenoid Wiring Diagram:

CANISTER PURGE VALVE CHECK

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 exists while the engine is running, the purge solenoid is energized:

1. The engine run time is more than one minute.
2. The coolant temperature is above 75~C or 167~F.
3. The vehicle speed is above 15 mph.
4. 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.

NOTE: Once the test sequence is completed, clear codes and verify NO "SERVICE ENGINE SOON" light exists.


CANISTER PURGE FUNCTIONAL TEST

TEST DESCRIPTION:

1. Apply a short length of hose to the lower tube of purge valve and blow air into it. Very little air should pass into canister, if any at all. If the canister has a constant purge orifice a small amount of air may go into canister. If air passes into canister, replace canister. If air does not pass into canister proceed to the next step.

2. Use a hand held vacuum pump and apply 15" Hg or 51 kPa of vacuum to the tube labeled "CONTROL VAC" on the purge valve diaphragm cover. The diaphragm should hold vacuum for at least 20 seconds. If it does not, replace the canister. If it does hold vacuum, proceed to the next step.

3. With vacuum still applied to the control vacuum tube, blow air into the lower tube. If air flow increased into the canister, the purge valve is OK. If air flow does not pass into the canister, the purge valve is bad and the canister must be replaced.


TANK PRESSURE CONTROL VALVE TEST

TEST DESCRIPTION:

1. Using a hand held pump, apply 15" Hg or 51 kPa of vacuum to the control tube. The diaphragm should hold vacuum for at least 20 seconds. If it does not hold vacuum, the diaphragm is bad and must be replaced.

2. Install a short piece of hose on the valve inlet tube (fuel tank side) and blow air into the hose. You should feel the diaphragm pop open and air should pass through the valve. If the valve does not open, it should be replaced.




INCORRECT OPERATION MAY CAUSE:

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.