Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
The Evaporative Emission (EVAP) control system leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay. The PCM monitors vacuum level via the fuel tank pressure sensor input. The PCM turns on the EVAP canister purge valve and EVAP vent solenoid, allowing engine manifold pressure to draw a small vacuum on entire EVAP system. If sufficient vacuum cannot be sustained over a given period of time, a small leak or a malfunction is suspected and DTC will set.