94 Fuel Tank Ventilation System (Major Leak) - Signal Implausible: Function

Fuel tank ventilation diagnosis is employed for detecting leaks in the fuel tank ventilation system. In this process, a pressure test is performed at idle speed and with the vehicle stationary.

The EVAP canister purge valve is opened and the shutoff valve closed. This causes a vacuum to build up in the tank, which is measured by the pressure sensor. If no vacuum builds up, a major leak is present. Diagnosis is then terminated.