P04B4
Refueling Vapor Control Valve Stuck Closed.
- 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
- B4
- FaultThe specific fault in that area
What it means
P04B4 means the engine control unit has judged that the refuelling vapour control valve is stuck closed. It commanded the valve open, usually during refuelling or an evaporative system test, and the pressure or flow feedback showed that vapour was not passing. The exact valve and test strategy vary by make, model and engine, so check the manufacturer's data for the vehicle.
Symptoms
- Malfunction indicator lamp on
- Fuel pump nozzle clicking off repeatedly or filling slowly at the pump
- Hiss or pressure release when opening the fuel cap
- Fuel smell around the filler or tank area
- Other evaporative emission codes stored alongside it
- Possible failure of an emissions test
Possible causes
- Valve mechanically stuck closed through dirt, corrosion or debrislikely
- Faulty valve solenoid or actuator that does not respond to the commandlikely
- Damaged wiring, poor connector contact or corrosion in the valve circuitpossible
- Blocked, kinked or crushed vapour line or restricted filler vent pathpossible
- Saturated or blocked carbon canister restricting vapour flowpossible
- Faulty fuel tank pressure sensor giving a false readingrare
- Fault inside the control unit driver circuitrare
How to diagnose
- Read the freeze frame data and note whether the code set during or after refuelling, and check for any other evaporative or fuel system codes
- Check the fuel cap seal and fit, and inspect the filler neck for damage or obstruction
- Inspect the valve wiring and connector for damage, corrosion, water ingress or pushed-out pins
- Visually check the vapour lines and canister area for kinks, crush damage, blockage or fuel contamination
- Run an actuator test on the valve and listen or feel for it operating, following the manufacturer's procedure
- Measure the valve coil resistance and compare it with the specification for that model
- Check for the correct supply voltage and control signal at the valve connector while it is commanded
- Compare the tank pressure sensor reading with expected values, then smoke test the evaporative system for leaks or restrictions if the valve checks out
How to fix
- Replace the refuelling vapour control valve if it is stuck or its coil is out of specification
- Repair or replace damaged wiring or connectors in the valve circuit
- Clear or replace blocked, kinked or damaged vapour lines and filler vent components
- Replace the carbon canister if it is saturated or restricted
- Replace the tank pressure sensor if it is proven faulty
- Clear the code after repair and confirm it does not return on a refuelling cycle and drive test
Can I keep driving?
Low severity
The car can normally be driven while you book it in for repair. Refuelling may be slow or awkward, and if you notice a strong fuel smell have it checked promptly.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.