01 Starting A Car Dealership Business: What You Need To Know • 02 ECU Tuning Explained: Understanding Stages, Benefits, and P… • 03 Before You Open A Car Dealership, Here Are Things Nobody Te… • 04 Converting a Petrol Car to LPG: Benefits, Process, and Cons… • 05 Why disc and drum brakes are used in the front and rear res… • 06 Engine Knock: Causes, Prevention, and Maintenance • 07 How Euro Standards Are Helping to Achieve Climate Change Go… • 08 Is It Bad to Drive Long Distances and Turn Off the Engine I… • 09 Why Dirty Grounds Cause More Car Problems Than People Reali… • 10 How to Warm Up Your Car Engine in Cold Weather •

DTC codes / P04xx · Auxiliary emission controls / P04C5

P04C5Fuel Fill Door Lock Position Sensor/Switch Circuit Low

P04C5 indicates that the powertrain control module (PCM) has detected a low-voltage condition on the fuel fill door lock position sensor circuit, meaning the signal wire is shorted to ground or the sensor's internal switch is stuck closed. The PCM expects a voltage within a specific range when the door is unlocked and a different range when locked, and this code sets when the voltage stays below the low threshold longer than calibrated.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • The fuel fill door may not lock or unlock with the central locking system, or it may lock unexpectedly.
  • A warning light on the dashboard, often accompanied by a message such as 'Check Fuel Fill Door' or 'Fuel Door Open'.
  • The fuel fill door may appear closed but the vehicle reports it as open, preventing remote start or causing an alarm.
  • In some vehicles, the fuel gauge or distance-to-empty calculation may behave erratically if the door status is used for evaporative system logic.
  • Often no symptoms besides the warning light, especially if the door still latches mechanically.

Common causes, most likely first

  1. A short to ground in the signal wire between the fuel fill door lock position sensor and the PCM, often due to chafed insulation or pinched wiring at the door hinge.
  2. A faulty fuel fill door lock position sensor or switch that remains closed when it should be open.
  3. Corrosion or water intrusion in the sensor connector or the inline connector near the fuel filler neck.
  4. A stuck or misadjusted fuel fill door lock actuator that keeps the sensor in the locked position.
  5. A poor ground connection for the sensor circuit, causing the PCM to read a false low voltage.
  6. Rarely, an internal fault in the PCM driver for that input circuit.

How to diagnose and fix it

  1. Verify the code with a scan tool and check live data for the fuel fill door lock position sensor while manually locking and unlocking the door.
  2. Inspect the sensor connector and wiring at the fuel fill door for corrosion, water intrusion, or physical damage, and clean or repair as needed.
  3. Disconnect the sensor and check the signal wire for continuity to ground with a multimeter; if grounded, trace and repair the short.
  4. Test the sensor's resistance or voltage output through its travel; replace the sensor if it does not change state correctly.
  5. Check the fuel fill door lock actuator for binding or sticking and replace it if it does not move freely.
  6. Clear the code and perform a road test with several lock/unlock cycles to confirm the repair.
  7. If the code persists after all circuit and component checks, consult the factory service information for PCM pinout and input testing before condemning the PCM.

Why this code often isn't the sensor

  • A chafed signal wire inside the rubber boot at the fuel door hinge is a frequent cause that looks like a failed sensor but is actually a wiring short.
  • The fuel fill door lock position sensor is often integrated into the latch assembly, so technicians replace the whole latch when only a small switch or wire is at fault.
  • On some vehicles, the fuel fill door status is used by the evaporative emissions system, and a false 'locked' signal can cause evap monitor failures without setting a fuel door code directly.
  • Water intrusion into the connector behind the fuel filler neck can create a low-voltage signal only in wet conditions, so the code may be intermittent and not present during a dry shop visit.
  • A binding fuel door lock actuator can hold the sensor in the locked position, setting P04C5 even though the sensor itself tests good on the bench.

Can I keep driving with P04C5?

The vehicle remains safe to drive because the fuel fill door lock is a convenience and emissions-related feature, not a safety system. Avoid forcing the fuel door open or closed if it is stuck, and have the circuit inspected soon to prevent water intrusion or a dead battery from a stuck actuator.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage