What does it mean?
The fuel filler door lock control circuit is the output the module uses to drive the actuator that locks the filler door, usually a small solenoid or motor that drives a pin into the latch. P04BB is stored when the module energises that output and detects no current flow, which is what an open circuit looks like from the driver's point of view. The cause lies in the wiring, the connector or the actuator winding rather than in a mechanism that is jammed, because a jammed lock still draws current. With the circuit open, the filler door cannot be locked with the vehicle and, on sealed tank systems, the module may also refuse to run evaporative tests that depend on a locked and confirmed closed door.
Symptoms
- Fuel filler door does not lock when the vehicle is locked
- No actuator sound at the filler door when the vehicle is locked or an output test is run
- MIL (check engine lamp) on with fuel filler door codes stored
- Security concern because the filler door can be opened by anyone
- Evaporative monitors that will not complete on vehicles requiring a confirmed locked state
Likely causes
- Open or broken wire between the module and the lock actuator, often from corrosion in the rear harness
- Actuator connector unplugged, partly seated or with a terminal pushed out
- Open winding inside the lock actuator solenoid or motor
- Corroded terminals in the exposed connector near the filler recess
- Blown fuse or open supply on the circuit feeding the door lock actuator
- Harness damage where it passes through the body grommet into the filler area
- Module driver stage failed open, considered only after external checks
How to fix it
- Run an output test with a scan tool and listen at the filler door for actuator movement
- Unplug the actuator and measure its winding resistance; an infinite reading identifies an open actuator
- Check for supply voltage at the harness connector with the ignition on, then test the control wire for continuity to the module
- Inspect the connector for corrosion, water, damaged seals and terminals that have backed out of their locks
- Follow the harness through the body grommet and along the rear of the vehicle, looking for corrosion, chafing and rodent damage
- Verify the supply fuse and any relay serving the lock circuit
- Repair the wiring or replace the actuator as indicated, then confirm the lock operates each time the vehicle is locked and unlocked