What it means
Same as P04B0 with the control line shorted to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
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 opens a vapor route to the canister during refueling. P04B1 sets when the module detects that the valve control circuit is held lower than expected, often because its control wire is shorted to ground or a connector has poor contact.
Common causes
Most likely first.
- Control line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Fuel vapors may escape during refueling
- Fuel odor around the filler area
- Refueling may be interrupted or difficult
How to diagnose it
- Check freeze-frame and EVAP data to confirm the fault concerns the refueling vapor control valve circuit.
- Inspect the valve connector and nearby tank or filler harness for chafing, moisture, corrosion, or loose and pushed-back terminals.
- With the circuit isolated as directed by the service information, test the control wire for a short to ground.
- Check connector condition and wiring continuity to find excessive resistance or damage in the valve control path.
- Test the valve and module-side circuit against the manufacturer's specification before replacing either component.
Common fixes
- Repair the valve control wire where it has contacted ground.
- Clean or replace corroded or loose connector terminals.
- Repair damaged insulation and secure the harness away from rubbing surfaces.
- Replace the refueling vapor valve if testing identifies an internal electrical fault.
Can I keep driving?
Avoid refueling if vapor is escaping or the filler behaves abnormally, and keep ignition sources away from any fuel odor. Driving may be possible when there is no leak, but the fault can prevent proper vapor capture and cause an emissions failure.
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.