Circuit Description

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

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

The EVAP emission system is checked by applying vacuum to the EVAP emission 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 emission canister purge valve and the EVAP emission 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 emission 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 P0442 to be set.