Faulty EVAP vent valve (internal coil open circuit or short); Damaged, chafed or corroded wiring to the vent valve, such as a short to voltage or an open circuit; Corroded, loose or water-contaminated connector at the vent valve or control unit; Blocked or contaminated vent valve or vent line causing the valve to stick or draw abnormal current; Fault in the engine control unit output driver for the vent valve; Blown fuse or fault in the supply feed to the valve circuit (depends on model wiring).

P0499

EVAP System Vent Valve Control Circuit High.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
99: FaultThe specific fault in that area

What it means

P0499 means the engine control unit has detected a high voltage state in the control circuit for the evaporative emission (EVAP) vent valve. The vent valve normally sits open to let fresh air into the charcoal canister and closes during leak tests. The code sets when the circuit voltage is higher than expected for the commanded valve state, which points to a wiring, connector or valve fault rather than a leak.

Symptoms

Malfunction indicator lamp on
Failed emissions or readiness monitor for the EVAP system not completing
Difficulty filling the fuel tank, with the pump clicking off repeatedly
Fuel smell around the rear of the car or fuel tank area
Possible slightly raised tank pressure noise when the filler cap is opened

Possible causes

Faulty EVAP vent valve (internal coil open circuit or short)likely
Damaged, chafed or corroded wiring to the vent valve, such as a short to voltage or an open circuitlikely
Corroded, loose or water-contaminated connector at the vent valve or control unitpossible
Blocked or contaminated vent valve or vent line causing the valve to stick or draw abnormal currentpossible
Fault in the engine control unit output driver for the vent valverare
Blown fuse or fault in the supply feed to the valve circuit (depends on model wiring)rare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including any other EVAP codes
Visually inspect the vent valve, its connector and the wiring near the fuel tank and canister for damage, water ingress, corrosion or road debris
Check the vent line and canister area for blockages, crushed hoses or insect nests
Using a scan tool with bi-directional control, command the vent valve open and closed and listen or feel for a click
Measure the valve coil resistance and compare it with the manufacturer specification for your model
Check the supply voltage and ground at the vent valve connector with the ignition on, using the wiring diagram for the vehicle
Test the control wire for shorts to voltage or open circuit between the valve and the control unit
Clear the code and road test, then confirm the EVAP monitor runs and the code does not return

How to fix

Replace the EVAP vent valve if the coil resistance or operation is out of specification
Repair or replace damaged wiring and fix any short to voltage or open circuit
Clean, dry and reseat or replace corroded or damaged connector terminals
Clear or replace a blocked vent line or contaminated canister components as found
Replace the engine control unit only after all wiring and the valve are proven good and the driver fault is confirmed

Can I keep driving?

Low severity

The car can normally be driven as usual, as this fault affects the emissions system rather than engine safety. Book it in soon, as it will cause an MOT emissions concern and may make refuelling difficult.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.