What it means
The control module monitors the electrical voltage in the EVAP vent valve control circuit. It sets this code when that voltage is above the expected range.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The EVAP vent valve controls air access to the charcoal canister, including during system leak checks. The control module monitors the valve's control-circuit signal; P0499 sets when that signal is higher than expected, commonly because the circuit is open or shorted to voltage.
Common causes
Most likely first.
- Vent valve control circuit open or shorted to voltage
- Vent valve solenoid fault
- Connector or wiring fault
Symptoms
- Check engine light on
- Possible smell of fuel near tank or engine bay
- Failed emissions inspection
- Loose-cap warning may appear
How to diagnose it
- Check freeze-frame data and related EVAP codes to see when the control module detected the high circuit signal.
- Inspect the vent-valve connector and wiring for a loose terminal, broken conductor, corrosion, or insulation damage that could expose the wire to voltage.
- Use the wiring diagram to check the vent-valve circuit for continuity and for an unintended connection to power.
- Command the vent valve with a scan tool and measure the control-circuit response against the manufacturer's specification.
- If the harness tests correctly, test the vent-valve solenoid and module control path according to the vehicle's wiring information.
Common fixes
- Reconnect or clean a loose or corroded vent-valve connector.
- Repair an open control wire or a wire shorted to voltage.
- Replace a vent-valve solenoid that fails its electrical test.
- Repair a confirmed module control-circuit fault.
Can I keep driving?
The vehicle is generally drivable, but the EVAP system may not seal or complete its self-checks, risking an emissions-test failure. Investigate a persistent fuel smell promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.