FUEL TANK LEAK DETECTION, VEHICLES WITH Fuel Tank Pressure Sensor -G400-

• The function of the leak detection system is based on the premise that the fuel system creates a natural vacuum when the fuel in the fuel tank becomes colder.
• The Fuel Tank Pressure Sensor -G400- -item 3- senses the vacuum in the vent line -4- near the EVAP canister -1-. The Fuel Tank Leak Detection Control Module -J909- -item 7- is attached directly to the wall of the fuel tank -6- and monitors the temperature inside the fuel tank. The system is considered to be sealed if the measured vacuum is 2.5 mbar. If there is no vacuum, then there is a leak in the fuel system, which will result in an entry in the engine control module DTC memory.

  Courtesy of AUDI OF AMERICA, LLC

2 -  Signal Wire to Engine Control Module -J623-

5 -  Bleeder Line to Engine