Powertrain, generic · Auxiliary emission controls

P0499 EVAP System Vent Valve Control Circuit High

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. The vent valve is normally open and switched to ground by the module (GM scheme P0449/P0498/P0499; Ford uses P0446). P0499 means the control wire is shorted to positive: with the driver on the output stays high – GM sees 0.5 Ω or less to the supply, Saab above 4.6 V; MIL after two trips. The valve then cannot close, the system cannot be sealed, and the leak tests are suspended because they would otherwise report a large leak.

Likely causes

Control wire touching battery positive or the valve supply (chafed harness)
Vent valve coil with shorted turns, driver switches off
Moisture or corrosion in the connector
Driver in the engine module

Symptoms

  • Check engine light on
  • EVAP 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.

Parts involved

evap vent valvevent valve wiringengine control module

Related codes

P0449P0498P0446P0448P0455P0459

References: gsi.ext.gm.com, saabwisonline.com, law.cornell.edu.