Circuit Description

When running the DTC P0442 Evaporative Emission (EVAP) System Small Leak Detected diagnostic detects evaporative emission system leaks as small as 0.020 in. Hg. The Powertrain Control Module (PCM) will command the EVAP vent valve ON, CLOSED, and the purge valve and the vacuum pressure switching valve ON, OPEN, with the engine running. This allows engine vacuum into the EVAP system. The PCM then commands the purge valve OFF, CLOSED, sealing the system. The PCM then monitors the fuel tank vapor pressure sensors signal to determine if there is vacuum decay. A rise or increase just above normal pressure indicates there is a small leak in the evaporative emission system. If the PCM detects the vacuum level was not achieved and vacuum decay was within a specified value a DTC P0442 will set.