P0449: EVAP System Vent Valve Control Circuit/Open
Standardized SAE J2012 code · P04xx — Auxiliary emission controls
What does P0449 mean?
The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0449 belongs to the newer scheme for the vent valve circuit – P0449 open, P0498 low, P0499 high – used mainly by GM and also by VW. The normally open valve is fed from the battery and switched to ground; with the driver off, the output should show supply voltage. A floating 2.6–4.6 V, or an impedance of 200 kΩ or more, means an open circuit (GM: 20 of 25 samples, MIL after two trips). The leak test and the vent performance check P0446 are then suspended; purging continues.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
Symptoms
- Check engine light on
- EVAP leak test does not run, readiness not set
- Usually no change in driving
Common causes
- High Vent valve connector (usually at the canister or tank, underbody) corroded or loose
- Medium Vent valve coil open
- Medium Supply (fuse) or control wire open
- Low Driver in the engine module
Likelihood is a general estimate across vehicles; your make and model may differ.
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