P0499 EVAP vent valve: signal or voltage too high

By: Diagno editorial team · Updated: 2026-10-15

P0499 means: EVAP vent valve: signal or voltage too high. Fuel vapour from the tank is collected in a charcoal canister and burnt in the engine. OK to drive, but have it checked soon. The most common repair costs about €45–90 in Estonia, depending on make and model.

What it means

Fuel vapour from the tank is collected in a charcoal canister and burnt in the engine. The computer found a leak or a valve fault in this system. It usually doesn't affect driving. The signal voltage is too high. Usually a wire is shorted to power, the ground is broken or the part itself has failed.

What you may notice

• Engine light on
• Sometimes a faint fuel smell
• The pump nozzle may click off early when filling

What could be wrong

1. 1Connector loose, damp or corroded · Wiring or connector repair €45–90
2. 2Wire shorted to power or ground broken · Wiring or connector repair €45–90
3. 3Faulty valve · Valve replacement €90–180
4. 4Engine computer fault (rare) · Control unit check and software €150–300

Repair difficulty: Easy

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Tighten the fuel cap until it clicks. If you smell strong fuel, have it checked straight away. You can do the simpler checks yourself.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the valve

Standard SAE description: Evaporative Emission System Vent Valve Control Circuit High