System Description

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

At appropriate time, EVAP canister purge valve and EVAP vent solenoid are turned ON, allowing engine to draw a small vacuum on entire EVAP system. After desired vacuum level has been achieved, EVAP canister purge valve is turned OFF, sealing system.

A restricted or blocked EVAP canister vent path is detected by drawing a vacuum on EVAP system, turning OFF EVAP vent solenoid and EVAP canister purge valve (EVAP vent solenoid Open, EVAP purge PWM 00) and monitoring fuel tank vacuum sensor input. With EVAP vent solenoid open, any vacuum in system should decrease quickly unless vent path is blocked. A blockage can be caused by following conditions:

1. Faulty EVAP vent solenoid (stuck closed).
2. Plugged kinked or pinched vent hose.
3. Shorted EVAP vent solenoid driver circuit.
4. Plugged evaporative canister.
5. If any of these conditions are present. Diagnostic Trouble Code (DTC) P0446 will set.