P0499 Evaporative Emission System Vent Valve Control Circuit High

P0499 indicates a high condition in the EVAP vent valve control circuit. The controller sees vent valve control voltage or feedback above the expected range.

Code details

Generic OBD-II · P0

System: Emissions
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not condemn the controller before checking vent valve ground, wiring, and short-to-voltage faults.

Symptoms of P0499

Check-engine light, often with no obvious change in how the car drives.
A failed emissions test or incomplete readiness monitors.
Sometimes a faint fuel-vapour smell (on EVAP codes).

Common causes of P0499

A worn catalytic converter or an oxygen/air-fuel sensor reading out of range.
EVAP leaks — a loose or failed gas cap, cracked hose, or purge/vent valve.
Exhaust leaks, fuel-trim problems, or a fault in a related monitor.

Useful checks before replacing parts

Review vent valve command, control voltage, driver status, current draw, EVAP pressure behavior, freeze-frame data, and related EVAP circuit codes.
Inspect for short-to-voltage faults, open grounds, connector corrosion, damaged wiring at the canister area, stuck valve load, and water intrusion.
Command the vent valve while measuring circuit response and verifying the EVAP system can seal and vent correctly.

Related OBD-II codes

These nearby emissions entries can help compare wording and pin down the fault area.