P0446Powertrain
Powertrain · SAE
EVAP System — Vent Control Circuit Malfunction
Meaning
The ECU detects an anomaly in the circuit of the canister vent valve (vent solenoid). The valve cannot correctly control EVAP system pressure during leak-detection tests or purge operation.
Common causes
- Vent valve stuck closed (prevents pressure equalization)
- Vent valve stuck open (prevents pressurization during leak test)
- Open or shorted electrical circuit of the vent valve
- Clogged air inlet filter or screen on the vent valve
- Damaged wiring or corroded connector at the vent valve
Symptoms
- Malfunction indicator lamp (MIL) on
- EVAP leak detection monitor failure
- Possible fuel odor near the fuel tank or canister
- Generally no driveability symptoms
- Evaporative emissions above regulatory limits
Severity
Moderate: the evaporative emission control system is compromised, resulting in hydrocarbon emissions above regulatory limits.
What to do
- Check the vent valve electrical circuit: supply voltage, ECU command signal, wire continuity
- Actuate the vent valve with a scan tool to verify mechanical operation
- Inspect the valve air inlet filter/screen for blockages
- Check connector and wiring for corrosion, shorts, or open circuits
- Replace the vent valve if mechanically or electrically faulty