System 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 restricted or blocked EVAP emission canister vent path is detected by drawing a vacuum on the EVAP emission system, turning OFF the EVAP emission vent solenoid and the EVAP emission canister purge valve (EVAP emission vent solenoid Open, EVAP emission purge PWM 0%) and monitoring the fuel tank vacuum sensor input. With the EVAP emission vent solenoid open, any vacuum in the system should decrease quickly unless the vent path is blocked. A blockage can be caused by the following conditions:
- Faulty EVAP emission vent solenoid (stuck closed)
- Plugged kinked or pinched vent hose
- Shorted EVAP emission vent solenoid driver circuit
- Plugged evaporative canister
- If any of these conditions are present, DTC P0446 will set.