Fuel Cap Lamp Control Circuit
Diagnostic trouble code P0624 indicates that the powertrain control module (PCM) has detected a malfunction in the control circuit for the fuel cap warning lamp. The PCM sets this code when the voltage signal from the fuel cap lamp circuit does not match the expected parameters, indicating an open, short, or excessive resistance in the circuit.
This code does not affect the drivability or safety of the vehicle. However, it should be repaired so the driver can be properly alerted if the fuel cap is loose or missing, which can cause evaporative emission leaks.
Common symptoms
- Illuminated Check Engine Light (MIL)
- Fuel cap warning lamp fails to illuminate during the bulb check at startup
- Fuel cap warning lamp stays illuminated continuously
- Fuel cap warning lamp flickers intermittently
- No noticeable drivability issues
Likely causes
- Burned out fuel cap warning lamp bulb or faulty LED
- Corroded, damaged, or loose wiring and connectors in the lamp control circuit
- Short to ground or voltage in the fuel cap lamp circuit
- Faulty instrument cluster
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Perform a visual inspection of the instrument cluster during the key-on, engine-off (KOEO) bulb check.
Look for: Observe if the fuel cap warning lamp illuminates. If it does not, the bulb or LED may be burned out, or there is an open circuit.
Inspect the wiring harness and connectors between the PCM and the instrument cluster.
Look for: Look for chafed wires, corrosion, bent pins, or loose connections that could cause an open or short circuit.
Test the fuel cap lamp bulb or LED directly, if accessible.
Look for: Check for continuity across the bulb. If there is no continuity, the bulb is blown and needs replacement.
Use a digital multimeter to check for voltage and ground at the instrument cluster connector for the lamp circuit.
Look for: Verify that the circuit receives the proper voltage and ground signals when commanded by the PCM or a bidirectional scan tool. Lack of signal indicates a wiring issue or PCM fault.
Use a bidirectional scan tool to command the fuel cap lamp on and off.
Look for: If the scan tool can turn the lamp on and off, the wiring and bulb are likely good, and the issue may be intermittent or related to the PCM's internal logic.
This page explains the generic P0624 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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