Circuit Description

The evaporative (EVAP) emission system is checked by applying vacuum to EVAP emission system and monitoring for a vacuum fault. The powertrain control module (PCM)/engine control module (ECM) monitors vacuum level through fuel tank pressure sensor signal. At an appropriate time, EVAP emission canister purge valve and EVAP emission vent solenoid are turned ON. allowing engine to draw a small vacuum on entire evaporative emission system. After desired vacuum level has been achieved. EVAP emission canister purge valve is turned OFF. sealing system. A leak is detected by monitoring for a decrease in vacuum level over a given time period. when all other variables remain constant. A leak. blockage or faulty component in system will cause a diagnostic trouble code (DTC) to be set.