Circuit Description

The evaporative emission (EVAP) system includes the following components:

• Fuel tank
• EVAP vent solenoid
• Fuel tank pressure sensor
• Fuel pipes and hoses
• Fuel vapor lines
• Fuel cap
• EVAP canister
• Purge lines
• EVAP canister purge valve
• EVAP service port

The evaporative emission system is checked by applying vacuum to the EVAP system and monitoring for a vacuum decay. The engine control module (ECM) monitors the vacuum level through the fuel tank pressure sensor signal.

At the appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge valve is turned OFF, sealing the system. A leak is detected by monitoring for a decrease in the vacuum level over a given time period, when all other variables remain constant. A small leak in the system will cause DTC P0456 to be set.