Evaporative Emissions System: Testing and Inspection

Functional Check:

Fuel Tank Pressure Control Valve:

Fuel Tank Pressure Control Valve
With hand vacuum pump, apply approximately 38 cm Hg (15" Hg) to the control vacuum tube. After ten seconds, there should be at least 13 cm Hg (5" Hg) vacuum remaining. If after 10 seconds there is less than specified vacuum, replace the valve.

With 38 cm Hg (15" Hg) applied to control vacuum tube, attach a short piece of hose to the valves tank tube side. Blow into the tube. You should feel air pass through the valve. If not, replace the valve.

Inspect
Ensure all connections and vacuum lines are tight and free of cracks, damage and restrictions. Visually check vapor canister for cracks and/or damage.

Canister Purge Test:

Canister Purge Solenoid Circuit:

Circuit Description
Canister purge is controlled by a solenoid that allows manifold vacuum to purge the fuel vapor canister when energized. The ECM supplies a ground to energize the solenoid. If the diagnostic "test" terminal is grounded with the engine stopped and ignition "ON", or the following conditions are met with the engine running, the purge solenoid will be energized (purge "ON").

^ Engine run time after start more than 1 minute
^ Coolant temperature above 60°C (140°F)
^ Vehicle speed above 2 mph
^ Throttle off idle, above 3%
^ IAT is less than 105°C (221°F)

Canister Purge Solenoid Check Chart C-3:

Test Description
Numbers below refer to circled numbers on the diagnostic chart.

1. Checks to see if the solenoid is opened or closed. The solenoid is normally closed and should open when the diagnostic test terminal is grounded.

2. Completes functional check by grounding the diagnostic "test" terminal. This should energize the solenoid and allow the vacuum to drop (purge "ON").

3. Checks for a complete circuit. Normally, there is ignition voltage on CKT 339 and the ECM provides a ground on CKT 428. A shorted solenoid could cause an open circuit in the ECM.

Diagnostic Aids
Normal operation of the canister purge solenoid described as follows:

^ With the ignition "ON", engine "OFF", diagnostic "test" terminal grounded, the canister purge solenoid should be energized.