FixItFor.Us
P codepowertrainLow severity

P0624Fuel Cap Lamp Control Circuit

The control module has detected an electrical fault in the circuit that operates the "Check Fuel Cap" indicator lamp.

Definition

Vehicles with a dedicated fuel cap warning indicator (common on Ford products) use it to alert the driver when the EVAP system detects a large leak consistent with a loose or missing fuel cap. The PCM monitors the lamp driver circuit for opens, shorts, and correct feedback, and sets P0624 when the circuit state does not match the command. The fault affects only the warning indicator — the engine runs normally — but a driver would not be alerted to a loose cap, and the associated EVAP leak would eventually set the MIL instead. This code refers to the lamp circuit itself, not the presence of an EVAP leak.

Common causes

  • Open or shorted wiring in the fuel cap lamp circuit between the PCM and cluster/indicator
  • Burned-out indicator bulb on discrete-lamp designs
  • Corroded or loose instrument cluster connector
  • Failed instrument cluster lamp driver
  • Failed indicator driver circuit inside the PCM

Common misdiagnoses

  • Replacing the fuel cap, which has no effect on a lamp circuit fault
  • Smoke-testing and repairing the EVAP system when no leak code is present
  • Replacing the purge or vent solenoid for what is an indicator wiring problem
  • Replacing the PCM before checking the lamp circuit and cluster

Troubleshooting steps

  1. 1.Separate lamp fault from EVAP fault

    Scan for EVAP codes (P0455/P0457); if none are present, the problem is confined to the indicator circuit, not the fuel cap or EVAP system.

  2. 2.Command the indicator with a scan tool

    Use PCM output control or the cluster self-test to toggle the fuel cap lamp and confirm whether it responds.

  3. 3.Check the lamp circuit wiring

    Test the control wire for continuity end to end and for shorts to ground or battery voltage, and inspect connectors at the cluster and PCM for damaged terminals.

  4. 4.Test the bulb or cluster

    On discrete lamps, check the bulb and socket; on integrated clusters, a failed self-test indicates a cluster repair or replacement.

  5. 5.Evaluate the PCM driver last

    If the wiring and cluster prove good and the PCM never toggles the circuit when commanded, the PCM's low-side driver has failed.

Related codes