P0499
EVAP System Vent Valve Control Circuit High
EVAP system
Generic OBD-II
Low
What it means
P0499 means the ECM sees a high voltage in the control circuit of the evaporative emission (EVAP) vent valve, which usually points to an open circuit. That valve lets fresh air into the charcoal canister during purge so trapped fuel vapours can be burned in the engine. The fault is an emissions-system issue only — the engine runs normally — so it mainly affects the check-engine light and emissions readiness.
Low
Can I keep driving? Safe to keep driving — this is an emissions/vapour-control fault that won't affect how the engine runs.
Common symptoms
What you'll notice
- Check-engine light on
- Usually no change in how the car drives
- May fail an emissions or EVAP readiness test
- Occasionally a faint fuel-vapour odour
Common causes
Most likely first
- Faulty EVAP vent valve solenoidLikely
- Open or high-resistance wiring/connector in the vent valve control circuit (a high signal often means an open)Common
- Corroded or loose connection at the vent valveCommon
- Engine control module (ECM) fault (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the code with a scan tool.
- Locate the EVAP vent valve (usually near the charcoal canister) and inspect its connector and wiring for an open.
- Measure the vent valve solenoid's resistance against spec.
- Replace the vent valve if the solenoid or circuit is faulty.
- Consider the ECM only after wiring and the valve test good. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0499?+
Yes. The EVAP vent valve only manages fuel vapour, so the engine runs normally. Repair it to clear the light and pass emissions.
Can I just clear P0499?+
It returns the next time the ECM runs its EVAP test unless the vent valve or its wiring is fixed.
Related codes
Often seen with P0499
Read & clear P0499 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX