Functional description of leak diagnosis

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The EVAP canister system (including the fuel tank) is equipped with a leak diagnostic system. This system detects leaks in breather system.

The diagnosis is based on the pressure principle and should detect leaks with a circumference larger than 1 mm.

During the diagnosis the fuel system Leak Detection Pump (LDP) -144- creates a pressure of 30 mbar in the EVAP system. When the pressure is attained the pump switches off. If the pressure drops below a predetermined value the pump switches on again. The On Board Diagnostic (OBD) monitors the switching periods and sets a fault in the Diagnostic Trouble Code (DTC) memory when the period is too short.

Observe safety precautions. Refer to Safety precautions when working on the fuel supply system .

Observe rules for cleanliness. Refer to Rules for cleanliness .

Servicing parts of the EVAP system. Refer to Engine code AEG .

Assembly overview of EVAP system. Refer to EVAP system, assembly overview .

NOTE:

Hose connections are secured with either spring-type or clamp-type clips.
Always replace clamp-type clips with spring-type clips.

Fig 1: Identifying Assembly Tool VAS 5024

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Assembly tool VAS 5024 or hose clip pliers V.A.G 1921 are recommended for installing spring-type clips.