Evaporative Emissions System: Testing and Inspection

CAUTION: Refer to Fuel Vapors in Evaporative Emission (EVAP) Components Caution in Service Precautions.

IMPORTANT: Before diagnosing any EVAP control system malfunction, perform a careful visual inspection of the EVAP control system components and of the connecting hoses.




1. Allow the engine to cool to room temperature.
2. Start the engine.
3. Disconnect the purge hose (1) from the EVAP canister purge valve (2).
4. Place a finger against the end of the disconnected hose in order to check for vacuum. Vacuum should not be felt if the engine temperature is below a normal operating temperature.
5. Connect the purge hose to the EVAP canister,and warm the engine to a normal operating temperature.
6. Disconnect the purge hose (1) from the EVAP canister purge valve (2).

IMPORTANT: The EVAP control system does not purge the EVAP canister unless the engine is sufficiently warmed up, and the Heated Oxygen Sensor (HO2S) is activated. When the purge hose is disconnected, as in Step 6, some air may be drawn into the purge line. As a result, the Powertrain Control Module (PCM) may detect a change in the purge gas concentration and may stop the purge. This is a normal action and may be the cause of a failure to detect vacuum in step 7. If vacuum is not present in Step 7, continued testing of the EVAP system may be necessary in order to avoid the replacement of good parts.

7. Place a finger over the disconnected hose in order to check for a vacuum. Vacuum should be felt with the engine running at normal operating temperature.

Failure of the EVAP control system to pass any of these checks indicates a possible malfunction that will require further inspection.