Circuit Description

WARNING: This page is about a different car, the 2002 Isuzu Trooper. However, it is still accessible from the selected car via links, so may be relevant.

Evaporative (EVAP) emissions system includes following components:

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.

Incorrect fuel tank pressure sensor signal is detected by monitoring fuel tank pressure when ignition is first turned on during cold start. If fuel tank pressure signal is out of range, DTC P0446 will set. A restricted or blocked EVAP vent path is detected by monitoring fuel tank pressure during normal operation (EVAP canister vent valve open, EVAP canister purge valve normal). With EVAP canister vent valve open, vacuum level in system should be very low unless vent path is blocked. A blockage can be cause by following conditions:

Faulty EVAP canister vent valve (closed).
Plugged, kinked or pinched vent hose.
Shorted EVAP canister vent valve driver circuit.
Plugged EVAP canister.

If any of the above conditions are present, DTC P0446 will set.

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

PCM will turn MIL off after DTC diagnostic runs and fault is no longer recognized. A history DTC P0446 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 PCM.