Error Code P0624 is defined as Fuel Cap Lamp Control Circuit. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, particularly those made since 1996 up to present. It’s particularly common among Chevrolet, Ford, GMC, Hyundai, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make, model, or powertrain configuration.

When Error Code P0624 is stored, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined a malfunction in the Fuel Cap Lamp Control Circuit.

The fuel cap is housed in the instrument panel, and its primary purpose is to warn the driver of loose or missing fuel cap when it lights up.

The PCM controls the fuel warning lamp, through input signal it receives from the fuel tank pressure switch and other sensors. The PCM can determine whether the fuel cap is installed correctly or not in the fuel filler neck. If the PCM determines a loose or missing fuel cap, then it registers the code and triggers the Check Engine light bulb.

The PCM usually monitors the continuity of the fuel cap lamp control circuit each time the engine is running.

Every time the ignition is on and the PCM is energized, both the APP sensor and TPS self-tests will commence. Aside from running the internal controller self-test, the CAN (controller area network) also compares signals from each module to ensure that each controller is running properly.

If the problem is determined while monitoring the fuel cap lamp circuit, then Error Code P0624 will be stored, and Check Engine light will be activated. Depending on the severity of the condition, it may take multiple failure cycles before the Check Engine light lights up.

Common Symptoms

  • Increased fuel consumption
  • Deactivation of the evaporative emission system

Other codes may be present as well.

Possible Causes

  • Defective or programming error in PCM
  • Open or shorted fuel camp lamp control circuit
  • Loose, missing, or defective fuel cap
  • Damaged fuel cap warning lamp bulb

How to Check

As with most error codes, diagnosing this fault requires a diagnostic scanner, battery/alternator tester, DVOM (digital volt/ohmmeter), and a reliable vehicle information source.

Look for the vehicle information from the TSB (technical service bulletin) that is parallel with the code stored, vehicle (year, make, and model), engine, and symptoms. If you find the right TSB, then this will give you the correct diagnostic information.

Start the diagnosis by connecting the scanner to the vehicle’s diagnostic port and retrieve all stored codes, as well as their freeze frame data. You may write this information down, in case the problem proves to be intermittent. After recording necessary data, clear the codes and then take the vehicle for a test drive until the code resets, or the PCM enters readiness mode. If the PCM enters Readiness Mode, that means the code is intermittent, and the problem must develop further before you can accurately diagnose and do the necessary repair. If the code resets, then continue with the diagnosis.

Use vehicle information source to obtain component locations, connector face views, connector pin-out charts, wiring diagram, and diagnostic flow chart related to your vehicle’s error code.

If all fuses and relays are running well, check whether the controller related wiring and harness are in order. You may also want to check chassis and engine ground junctions. Again, use your vehicle information source to obtain ground locations as related circuits. Test ground integrity using the DVOM.

Then, check the system controllers for any signs of water, heat, or collision damage. Any controller that is damaged, especially by water, is considered defective and must be replaced.

If controller power and ground circuits are intact, then there’s a good chance the controller is defective, or there’s a programming error in the controller. Thus, controller replacement requires reprogramming. In some cases, you may want to get aftermarket reprogrammed controllers. Some vehicles and controllers require on-board reprogramming that may be done only through the dealership or a qualified shop.

How to Fix

Depending on your diagnosis, common repairs for this code include:

  • Repair or replacement of faulty wiring and connectors
  • Test individual control modules
  • Use of Autohex or Tech II CAN bus tester to identify the specific area of the problem
  • Replacement of fuel cap, control circuits or connections
  • Replacement of CAN bus itself

Though this code may not stop the vehicle from running safely, it must not be ignored. This electrical problem could be detected through a long list of sensors and modules. And rather than allowing the issue to remain, it’s best to find where the electrical glitch is happening.

If the fuel cap doesn’t light up during KOEO (key-on-engine-off), then suspect a defective fuel cap warning lamp bulb.