Circuit Description

Evaporative (EVAP) emission system includes the following components, fuel tank, EVAP vent solenoid, fuel tank pressure sensor, fuel pipes and hoses, fuel cap, EVAP lines, EVAP canister and EVAP purge solenoid.

The evaporative leak detection diagnostic strategy is based on applying vacuum to EVAP system and monitoring vacuum decay. PCM monitors vacuum level through the fuel tank pressure sensor input. At a given time, the EVAP purge solenoid and EVAP vent solenoid are turned on, allowing engine vacuum to draw a small vacuum on the entire evaporative emission system. After desired vacuum level has been achieved, the EVAP purge solenoid is turned off, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a given time period, all other variables remaining constant. A small leak in the system will cause DTC to set.