Leak Detection System (Vehicles Through My 2012)

WARNING: This page does not describe the selected car, but rather 16 other vehicles, including the 2016 Audi S4, 2016 Audi A4 Quattro, 2016 Audi A4, 2015 Audi S4, and 2015 Audi A4 Quattro. 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, Evaporative Emission (EVAP) canister and 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 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 that the tank system is sealed.
If pressure falls (indicating a leak), the diaphragm moves back and the reed contact closes.
If the reed contact closes within the 15 seconds of detection time, a further test is performed. In this case the diaphragm pump pumps four 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 constant drive at a speed 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. In addition, the diagnostics can be activated via the Vehicle Diagnostic Tester. Refer to TANK LEAK DIAGNOSIS, PERFORMING, VEHICLES THROUGH MY 2012 .

NOTE:

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

It can be determined if an automatic leak diagnosis was recently performed with the Vehicle Diagnostic Tester connected in measured values block 071. Refer to TANK LEAK DIAGNOSIS, PERFORMING, VEHICLES THROUGH MY 2012 .