Circuit Description

PCM will test the EVAP system for the following conditions:

• Large and small leaks (P0440 and P0442).
• Excess vacuum (P0446).
• Purge flow during non-commanded conditions (P1441).
• Fuel pressure and level sensor faults (P0452, P0453, P0461, P0462 and P0463).
• EVAP purge and vent valve faults (P1645 and P1646).

PCM monitors the amount of vacuum in EVAP system by monitoring the fuel tank pressure sensor. For this DTC, PCM turns on both the EVAP purge and vent valves when conditions for setting this DTC are met. Engine vacuum is applied to closed EVAP system, checking whether vacuum can develop in EVAP system. Failure to develop vacuum may result from a large leak or from restriction. DTC will set after 2 consecutive failures during test.

DTC will set when EVAP system cannot develop vacuum.