Diagnostic Aids

Operate the vehicle under the condition of the customers concern. Under high temperature conditions, fuel vapors may increase to the point of EVAP canister vapor saturation. Fuel vapors would then be released into the atmosphere. Once the engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
Test for fuel leaking in the fuel tank and the fuel feed and return pipes.
Test for fuel vapor leaks in the fuel tank, fill limiter vent valve and rollover valves, the fuel fill pipe, hose and fuel fill cap, the fuel sender housing and seal, the Fuel Tank Pressure (FTP) sensor seal and the EVAP vapor pipe.
Movement of the EVAP pipes or fuel pipes may help find an intermittent condition.

Fig 1: Identifying Fuel Tank Cap Adapter (J 41415-40)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Identifying Evaporative Emission System Tester (J 41413-200)

Courtesy of GENERAL MOTORS CORP.

Fig 3: Identifying Ultrasonic Leak Detector (J 41416)

Courtesy of GENERAL MOTORS CORP.