Powertrain, generic · Auxiliary emission controls

P0449 EVAP System Vent Valve Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Vent valve connector (usually at the canister or tank, underbody) corroded or loose
Vent valve coil open
Supply (fuse) or control wire open
Driver in the engine module

Symptoms

  • Check engine light on
  • EVAP leak test does not run, readiness not set
  • Usually no change in driving

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–250
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Inspect connector
  2. Measure solenoid resistance

Parts involved

evap vent valvevent valve wiringengine control module

Related codes

P0498P0499P0446P0447P0448P0443

References: gsi.ext.gm.com, saabwisonline.com, gsi.ext.gm.com, static.nhtsa.gov.