Emissions

P0499 — EVAP Vent Valve Control Circuit High

Severity: low Safe to drive

What P0499 means

The EVAP system traps fuel vapors from the tank and sends them to the engine to be burned. The vent valve opens the system to fresh air through the charcoal canister and closes it during leak tests. P0499 sets when the control module sees a higher voltage than expected on the valve's control circuit, pointing to an electrical fault in the circuit or the solenoid.

Symptoms

  • Check engine light on
  • EVAP monitor not ready
  • Failed emissions test or inspection
  • Possible fuel smell if there is also a vapor leak
  • Fuel pump shutting off repeatedly while refueling

Possible causes

  1. Open circuit in the vent valve control wiring
  2. Failed vent valve solenoid
  3. Damaged or corroded wiring or connector
  4. Control wire shorted to battery positive
  5. Faulty control module (rare)

How to diagnose

  1. Read codes and freeze-frame data and look for other EVAP codes
  2. Check that the fuel cap is seated and not cracked
  3. Inspect the vent valve, connector and harness for damage, moisture and corrosion
  4. Measure the valve coil resistance and compare it with the specification
  5. Command the purge and vent valves with a scan tool and listen for the click
  6. Check power and control signal at the connector and test the circuit for opens and shorts to voltage
  7. Review fuel tank pressure sensor readings
  8. Smoke-test the EVAP system if leaks are suspected

Common fixes

  • Replace the EVAP vent valve
  • Repair or replace the damaged wiring or connector
  • Fix any short to positive voltage
  • Replace the fuel cap if it is faulty
  • Clear the code and confirm it does not return after a test drive

Questions and answers

What does P0499 mean?

The control module detected a high voltage on the EVAP vent valve control circuit. The cause is most often the valve solenoid or its wiring.

Can I drive with code P0499?

Yes, for normal short-term driving it is generally fine. Still, repair it to keep vapor emissions down and pass inspection.

Can a loose gas cap cause P0499?

Unlikely, because this code points to an electrical circuit problem. The cap is still worth checking first, as it commonly causes other EVAP codes.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.