Component Tests and General Diagnostics

BASIC INSPECTION
Ensure all vacuum hoses and electrical wires are routed clear of the exhaust manifold to prevent deterioration due to the high temperature. Vacuum hoses should always be a minimum of three inches from the exhaust manifold. When replacing the charcoal canister, mark then disconnect vacuum hoses from charcoal canister to ensure proper installation.

NOTE: Use only fuel resistant hoses when servicing the evaporative control system.

ROLLOVER AND PRESSURE RELIEF VALVE
In vehicle rollover the valve is inverted. In this position the plunger is forced against the guide plate and raw fuel is prevented from flowing through the valve orifice into the fuel tank vent tube.

These vehicles are equipped with only one [1][2]rollover/pressure relief valve. These dual function valves relieve fuel tank pressure and prevent fuel flow through the fuel tank vent lines should the vehicle be rolled over. To test the To test the Purge Shutoff Switch perform the following procedure.

1. Inspect fuel and vapor hoses for proper routing, cracks, or restrictions.
2. Inspect fuel tank cap for proper seal and fit.
3. Remove fuel tank vent hose from EVAP Canister. Apply light air pressure (3-6 psi) to the Fuel tank filler tube. Air flow should be present at fuel tank vent hose. If air flow is not present, and Fuel Tank is not over-full, replace Pressure/Relief Rollover Valve.

EVAP PURGE SOLENOID
Vacuum to the Charcoal Canister is controlled by the EVAP Purge Solenoid. The Powertrain Control Module (PCM) operates the solenoid by switching the ground path on and off. To test the Purge Solenoid perform the following procedure.

1. Check electrical and vacuum hose connections. [1]
2. Remove solenoid electrical connector. Measure solenoid windings with high input impedance ohmmeter. Should be a minimum of 20 ohms.
3. Remove solenoid vacuum connector. Install a vacuum pump to the top port of solenoid. With a test lead apply 12 volts to one terminal of the solenoid and ground other terminal. Apply vacuum to solenoid, should vent to bottom port of solenoid. If vacuum did not vent replace solenoid.
4. Remove ground from solenoid. Apply vacuum to solenoid, should vent to middle port of solenoid. If vacuum did not vent replace solenoid.
5. To verify PCM is controlling the solenoid connect a voltmeter to 12 volt power supply (electrical connector installed). When de-energized volt-meter will read battery voltage. When energized voltmeter will read less than 1 volt.
6. Reconnect electrical and vacuum connectors.

[1] If solenoid winding resistance is less than 20 ohms PCM damage may result.

PURGE SHUTOFF SWITCH
A faulty Purge Shutoff Switch can result in increased emissions and/or poor driveability. To test the Purge Shutoff Switch perform the following procedure.

1. Check vacuum hoses for proper routing.
2. Remove fuel vapor hose from canister and plug.
3. Remove purge hose from intake manifold.
4. Remove vacuum signal hose from purge switch and install vacuum pump.
5. Blow on purge hose, passage should be closed. (If passage is open replace Purge Switch/Canister assembly).
6. Apply vacuum (15 in/Hg) to signal port of purge switch.
7. Blow on purge hose, passage should be clear. (If passage is closed replace Canister-Purge Switch assembly). 8. If Purge Switch is operating properly, reinstall vacuum and vapor hoses.

CHARCOAL CANISTER
The charcoal canister is a sealed service-free unit. [1]

[1] If Charcoal Canister is saturated with liquid fuel check for proper Purge Shutoff Switch and Pressure/Relief Rollover Valve operation.