P0499: EVAP System Vent Valve Control Circuit High

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.

Symptoms

• Check engine light on
• EVAP readiness not set
• Usually no change in driving

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Start with the fuel cap: tighten it fully and check its seal
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Inspect the hoses and connections around the tank and the charcoal canister
4. Use the scanner to test the purge and vent solenoid valves
5. Run a smoke test to find small leaks

Good to know

• Repair difficulty: easy
• It affects emissions.

What each character of P0499 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 4: Emissions
• 99: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0499?

Yes, you can normally keep driving. If there is a strong smell of gasoline, find the leak before continuing and do not smoke nearby.

What causes code P0499?

The most common causes are: 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.

Related codes

• P0449EVAP System Vent Valve Control Circuit/Open
• P0498EVAP System Vent Valve Control Circuit Low
• P0446EVAP System Vent Control Circuit
• P0448EVAP System Vent Control Circuit Shorted
• P0455EVAP System Leak Detected - Large Leak
• P0459EVAP System Purge Control Valve A Circuit High

Sources

• gsi.ext.gm.com: 18OBDG03A Engine Diagnostics
• saabwisonline.com: dtc p0449 p0498 or p0499 lau
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.