Fuel Tank Leak Detection

• The fuel tank leak detection function is based on the premise that the fuel systems creates a natural vacuum when the fuel in the fuel tank becomes colder.
• The Fuel Tank Pressure Sensor -G400- -1- senses the vacuum in the bleed line near the Evaporative Emission (EVAP) canister -2-. The Fuel Tank Leak Detection Control Module -J909- -4- is attached directly to the wall of the fuel tank -3- and monitors the temperature inside the fuel tank. The system is considered to be closed if the measured vacuum is 2.5 mbar (0.036 psi).
• There is a leak in the fuel system if there is not vacuum, which will result as an entry in the control module Diagnostic Trouble Code (DTC) memory.

5 -

Signal wire to the Engine Control Module -J623-

6 -

Bleed line to the engine

Fig 1: Identifying Fuel Tank Pressure Sensor, EVAP Canister, Fuel Tank And Fuel Tank Leak Detection Control Module

Courtesy of AUDI OF AMERICA, LLC