What it means
Same as P04B3 with the valve stuck closed - vapor cannot reach the canister during refueling, vapor escape from the filler is possible.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The refueling vapor control valve routes fuel vapor from the filler area to the charcoal canister while fuel is being added. The engine control module monitors the valve's operation during refueling. P04B4 sets when the valve is detected as stuck closed, restricting that vapor path.
Common causes
Most likely first.
- Valve stuck closed due to seal or debris
- Carbon or debris buildup preventing free movement
- Component wear with age - mechanical play
Symptoms
- Check engine light on
- Fuel odor near the filler or vehicle
- Fuel vapors may escape during refueling
- Refueling may be interrupted or difficult
How to diagnose it
- Check freeze-frame data and any refueling-related live data to see when the closed-valve fault was detected.
- Inspect the refueling vapor valve and its connections for dirt, carbon deposits, damage, or a visibly stuck mechanism.
- Check the valve connector and nearby wiring for loose pins, corrosion, or damage that could prevent the valve from operating.
- Use a scan tool to command the valve, if supported, and observe whether its reported state or vapor flow response changes.
- Test the valve's electrical circuit and mechanical movement according to the manufacturer's specification to distinguish a stuck valve from a control fault.
Common fixes
- Remove debris or carbon buildup that is preventing the valve from moving, if the valve is serviceable.
- Repair a loose, damaged, or corroded valve connector or wiring.
- Replace the refueling vapor control valve if it remains stuck closed or fails its circuit tests.
Can I keep driving?
You can usually drive if the vehicle runs normally, but refueling may be difficult and fuel vapors may escape near the filler. Avoid forcing fuel into a restricted filler, and address the fault promptly to limit vapor release.
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.