Evaporative Emissions System: Testing and Inspection

Fig. 36 Emission control system wiring circuit:

1. The ECM controls the operation of the canister purge control system. When the engine is cold, the ECM energizes the canister purge control solenoid, and vacuum to the canister purge control line is blocked. When the engine reaches operating temperature, the canister purge control solenoid is deenergized and vacuum is supplied to the canister purge control.
2. Connect vacuum gauge to vacuum supply hose at canister. With engine cold, check for vacuum with engine idling. If vacuum is present, proceed to step 3. If vacuum is not present, allow engine to run until normal operating temperature is reached, then check vacuum supply with engine idling at part throttle. If vacuum is present, system is operating properly. If vacuum is not present, proceed to step 3.
3. Stop engine, turn ignition on and enter Code .9.6. Disconnect canister purge electrical connector and connect test lamp between harness connector pins.
4. If lamp lights, check circuit 428, Fig. 36, for a short to ground. If circuit is satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary.
5. If lamp does not light, check 10 amp ignition fuse. If fuse is blown, repair short to ground in circuit 639 and replace fuse. If fuse is not blown, check for open in circuits 639 and 428. If circuits are satisfactory, measure resistance across canister purge solenoid in both directions. If both readings are less than 20 ohms, replace solenoid and ECM. If either reading is greater than 20 ohms, check for a faulty ECM or ECM connector and repair or replace as necessary.
6. If lamp flashes in three second intervals, check vacuum hoses for leaks or restrictions. If hoses are satisfactory, replace canister purge solenoid.