Fuel Cap Lamp Control Circuit
P0624 indicates a problem with the fuel cap lamp control circuit, which alerts drivers when the fuel cap is loose or missing. The PCM detects an open, shorted, or malfunctioning circuit in the fuel cap warning lamp system, preventing proper notification to the driver.
What You Might Notice
- Fuel cap warning lamp not illuminating when fuel cap is loose
- Fuel cap warning lamp staying on continuously
- Diminished fuel efficiency
- Evaporative emissions system deactivation
- Check Engine light illuminated
Most Common Causes
- 1
Fuel cap warning lamp bulb failure
The warning lamp bulb has burned out or is defective, preventing the circuit from completing properly and triggering the code.
- 2
Open or shorted fuel cap lamp control circuit
Broken wiring, loose connections, or damaged circuit traces in the fuel cap lamp control circuit prevent proper signal transmission from the PCM to the lamp.
- 3
Faulty or defective fuel cap
A loose, damaged, or missing fuel cap prevents proper sealing, causing the cap position sensor to trigger the warning lamp circuit abnormally.
- 4
PCM programming error or faulty PCM
Software corruption in the Powertrain Control Module or a defective PCM module may cause incorrect fuel cap lamp circuit operation or signal processing.
How to Diagnose It
- 1
Check Fuel cap warning lamp bulb failure — The warning lamp bulb has burned out or is defective, preventing the circuit from completing properly and triggering the code.
- 2
Check Open or shorted fuel cap lamp control circuit — Broken wiring, loose connections, or damaged circuit traces in the fuel cap lamp control circuit prevent proper signal transmission from the PCM to the lamp.
- 3
Check Faulty or defective fuel cap — A loose, damaged, or missing fuel cap prevents proper sealing, causing the cap position sensor to trigger the warning lamp circuit abnormally.
- 4
Check PCM programming error or faulty PCM — Software corruption in the Powertrain Control Module or a defective PCM module may cause incorrect fuel cap lamp circuit operation or signal processing.
How to Fix It
- 1
Inspect and replace fuel cap warning lamp bulb
Locate the fuel cap warning lamp in the instrument cluster, access the bulb socket, and replace with a new bulb of the correct specification. Verify the lamp illuminates properly after replacement.
- 2
Inspect fuel cap and seating surface
Remove the fuel cap and inspect it for cracks, damage, or missing seals. Clean the cap and fuel filler neck area, then reinstall the cap firmly until it clicks. Replace the fuel cap if damaged.
- 3
Test and repair fuel cap lamp control circuit
Use a digital multimeter to test for continuity and proper voltage in the fuel cap lamp control circuit wiring. Repair or replace any damaged wiring, corrosion at connectors, or loose connections between the PCM, lamp socket, and ground.
- 4
PCM reprogramming or replacement
If circuit testing is normal, reprogram the PCM using manufacturer diagnostic software and the latest calibration files. If reprogramming fails to resolve the issue, the PCM may be faulty and require replacement.
Need a deeper diagnosis?
Search for related repair guides or browse by system.