Open circuit, chafed or corroded wiring between the control unit and the fuel cap lamp or cluster; Poor connection or corroded terminals at the instrument cluster or control unit connector; Blown bulb or failed LED in the fuel cap lamp circuit, where it is a separate lamp; Short to earth or short to supply in the lamp control wire; Faulty instrument cluster or its internal driver circuit; Fault in the engine control unit output driver, or outdated software where the manufacturer has a known fix.

P0624

Fuel Cap Lamp Control Circuit.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
24: FaultThe specific fault in that area

What it means

P0624 is the generic code for a fault in the fuel cap lamp control circuit. The engine control unit drives a warning lamp that tells the driver the fuel filler cap is loose, missing or faulty. The code sets when the control unit sees a voltage or current at the lamp output that does not match the state it commanded, such as an open circuit, short to earth or short to supply. Not every vehicle has a dedicated fuel cap lamp, so how it is wired and displayed depends on the model.

Symptoms

Fuel cap warning lamp stays on, or never lights during the bulb check
Fuel cap message missing or incorrect on the instrument cluster
Malfunction indicator lamp may be on
No obvious change in how the engine runs
Possible related evaporative emission codes stored alongside

Possible causes

Open circuit, chafed or corroded wiring between the control unit and the fuel cap lamp or clusterlikely
Poor connection or corroded terminals at the instrument cluster or control unit connectorlikely
Blown bulb or failed LED in the fuel cap lamp circuit, where it is a separate lamppossible
Short to earth or short to supply in the lamp control wirepossible
Faulty instrument cluster or its internal driver circuitpossible
Fault in the engine control unit output driver, or outdated software where the manufacturer has a known fixrare

How to diagnose

Read all stored codes and freeze frame data, and note whether any evaporative emission or fuel cap codes are also present
Check the fuel filler cap is fitted, undamaged and tightened correctly, then see whether the lamp behaves normally
Watch the lamp at ignition on to see if it completes a bulb check, and note whether it stays on or stays off
Inspect the wiring and connectors between the control unit and the instrument cluster for damage, water ingress, corrosion or pin tension problems
Using the wiring diagram for the specific model, test the lamp control wire for continuity, short to earth and short to supply
Check the supply and earth feeds to the lamp or cluster and the condition of the bulb or LED if serviceable
Use a scan tool's output test, if the vehicle supports it, to command the lamp on and off and compare with the control unit's reading
Check for applicable software updates or technical bulletins for the model if the wiring and cluster test good

How to fix

Repair or replace damaged wiring and clean or renew corroded connector terminals
Replace the failed bulb or LED where the lamp is serviceable
Replace or repair the instrument cluster if its driver circuit is faulty
Replace or repair the engine control unit only after the wiring and cluster are proven good
Apply a manufacturer software update if an outdated calibration is a known cause for that model
Replace a damaged fuel filler cap if it is also causing related warnings, then clear the code and confirm it does not return

Can I keep driving?

Low severity

The car can normally be driven as the fault affects a warning lamp circuit rather than engine operation. Book it in soon, as the lamp may not warn you about a loose fuel cap and the MOT may be affected if the warning lamp stays on.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.