Evaporative Emissions System: Service and Repair

Leak Detection System

Function

The leak detection system recognizes leaks in the complete fuel system, including the fuel tank, EVAP canister and Evaporative Emission (EVAP) Canister Purge Regulator Valve 1 (N80).

On the mechanical side, the leak detection system consists mainly of a vacuum-driven diaphragm pump, that is equipped with a reed contact on the actuation rod of the pump diaphragm. The pump is supplied with vacuum via the mechanical vacuum pump or the engine intake stroke.

• When the leak detection is activated, the diaphragm pump pumps the fuel system up to 20 to 30 mbar. The pump diaphragm is then moved out so that the reed contact at the operating rod remains in the "open" position.

• During leak diagnosis, the reed contact is monitored to check if it remains open within 15 seconds. This indicates the fuel system is sealed.

• If pressure falls (indicating a leak), the diaphragm moves back and the reed contact closes.

• If reed contact closes within 15 seconds of leak detection time, a further test is performed: In this case the diaphragm pump pumps 4 times again. The Engine Control Module (ECM) measures the time for each of the 4 pumps until the reed contact is closed again. From that, the control module can recognize a "small leak" (smaller than 1 mm in diameter) or a "large leak".

The leak detection is activated automatically, shortly after each cold engine start (under 35 °C (95 °F)) and a continual drive faster than 10 km/h. In case a fault is detected, a Diagnostic Trouble Code (DTC) will be stored to memory. The Malfunction Indicator Lamp (MIL) in the instrument cluster lights up if the malfunction is recognized for 2 subsequent starts. Leak diagnosis can also be activated using the vehicle diagnosis, testing and information system (VAS 5051B). Refer to => [ Leak Detection Test, Performing ] Diagnosis and Testing.

• After the cold start, the leak detection can be repeated up to 10 times within the first 20 minutes.

• It can be determined if an automatic leak diagnosis was recently performed by using the (VAS 5051B) in measured value block 071. Refer to => [ Leak Detection Test, Performing ] Diagnosis and Testing.