Leak Detection System

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2012 Audi S5, 2011 Audi S5, 2010 Audi S5, 2010 Audi A5, and 2009 Audi S5. However, it is still accessible from the selected car via links, so may be relevant.

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 -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 mechanical vacuum pump or engine intake stroke.

When leak detection is activated, the diaphragm pump pumps 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 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) and a continual drive faster than 10 km/h. In case a fault is detected, a 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 Vehicle Diagnosis, Testing and Information System:VAS 5051B PERFORMING DIAGNOSTIC LEAK TEST .

NOTE:

After the cold start, the leak detection can 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 Vehicle Diagnosis, Testing and Information System:VAS 5051B in measured value block 071 PERFORMING DIAGNOSTIC LEAK TEST .