Circuit Description

Following components are included in Evaporative (EVAP) system:

• Fuel tank.
• EVAP canister vent (cut) valve.
• Fuel Vapor Pressure (FVP) sensor.
• Fuel pipes and hoses.
• Vapor lines.
• Fuel filler cap.
• EVAP emissions canister.
• Purge lines.
• EVAP canister purge valve.

EVAP leak detection diagnostic strategy is based on applying vacuum to EVAP system and monitoring vacuum decay. ECM monitors vacuum level via Fuel Vapor Pressure (FVP) sensor input. At an appropriate time, EVAP canister purge valve and EVAP canister vent valve are turned ON, allowing engine vacuum to draw a small vacuum on entire EVAP system. After a desired vacuum level has been reached, EVAP canister purge valve is turned OFF, sealing system. A leak is detected by monitoring for a decrease in vacuum level over a given period of time, all other variables remaining constant. A small leak in system will cause DTC P0456 to set.

When DTC sets, ECM illuminates MIL on second trip after fault was detected. ECM will store conditions present when DTC was set as freeze frame data in the FAILURE RECORDS data.

ECM will turn MIL off on third consecutive trip cycle during which diagnostic runs and fault is no longer recognized. A history DTC P0456 will clear after 40 consecutive trip cycles during which diagnostic runs and fault is no longer recognized. DTC can be cleared with scan tool, or by disconnecting battery voltage feed to ECM.