Function of leak diagnostic

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The EVAP canister system (incl. fuel tank) is equipped with a leak diagnostic that detects leaks (improper seal) in the system.

The diagnostic is based on pressure characteristics and is intended to detect leaks with diameters greater than 1 mm.

During the diagnostic, the Leak Detection Pump (LDP) -V144- generates a positive pressure of approx. 30 mbar in the EVAP canister system. The pump is switched off once the pressure is reached. If pressure falls below a specified value, the pump is switched on again. On Board Diagnostic monitors the switch intervals and stores a DTC in DTC memory if the intervals are too short.

Vehicles with engine code BJS

Before each leak diagnostic, Evaporative Emission (EVAP) Canister Purge Solenoid Valve -N115- is opened briefly to release any positive pressure present.

NOTE:

Hose connections are secured with screw-type clamps, spring-type clamps or tensioning clamps.
Always replace tensioning clamps with spring-type clamps or screw-type clamps.
Fuel hoses at engine must only be secured with spring-type clamps. The use of clamping collars or screw clamps is not permitted.

Fig 1: Spring-Type Clip Pliers VAS 5024A

Courtesy of VOLKSWAGEN UNITED STATES, INC.

NOTE:

VAS 5024A spring clip installation tool is recommended for installing spring-type clips.
Engine Control Module (ECM) is equipped with On Board Diagnostic (OBD).
Components marked with * are tested via On Board Diagnostic (OBD). Refer to Diagnostic mode 3: Check DTC Memory

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

Observe rules for cleanliness. Refer to Rules of cleanliness .

Parts of EVAP canister system, removing and installing:

Vehicles with engine code AFP. Refer to Parts of EVAP canister system (vehicles with engine code AFP), removing and installing ,
Vehicles with engine code BDF. Refer to Parts of EVAP canister system (vehicles with engine code BDF), removing and installing ,
Vehicles with engine code BJS. Refer to Parts of EVAP canister system (vehicles with engine code BJS), removing and installing .

Overview plan of EVAP canister system:

Vehicles with engine code AFP. Refer to Overview plan of EVAP canister system (vehicles with engine code AFP) ,
Vehicles with engine code BDF. Refer to Overview plan of EVAP canister system (vehicles with engine code BDF) .

EVAP canister system, checking for proper seal. Refer to Evaporative Emission (EVAP) canister system, checking for proper seal .