SPN 4124 - Fuel Level Sensor Circuit Low
Indicates a low fuel level sensor signal in the fuel tank.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The fuel level sensor is telling the engine computer that the fuel level is too low, which could cause running issues.
What the computer is actually seeing
The ECM sees a valid signal from the fuel level sensor that drops below the expected minimum value, usually below 0.5 volts or corresponding resistance levels.
What a healthy reading looks like
Fuel level sensor should provide a voltage between 0.5V (empty) and 4.5V (full).
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the fuel level reading on the dash: Is it showing empty? If yes, fill tank with fuel to see if reading changes.
- 22. Inspect wiring and connectors for the fuel level sensor: Look for cuts, corrosion, or disconnections. Are they in good condition?
- 33. Test the fuel level sensor with a multimeter: Disconnect the sensor, and measure the resistance/voltage while moving the float. Do you get varying readings from 0.5V to 4.5V?
- 44. Check the ground connection at the sensor: Is there continuity to a known good ground?
- 55. If sensor tests good, verify the ECM input reading: Use a scan tool to check for live data. Does it show correct voltage following the sensor values?
Common causes
- Faulty fuel level sensor
- Wiring issues or short circuit
- Bad ground connection
- Incorrect fuel level gauge calibration
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate severity; you may experience reduced performance. It's better to fix it soon.
Will this code come back after resetting?
If the underlying issue is not fixed, it will likely return.
Why does this code appear alongside other codes?
Multiple codes can indicate related problems, like fuel level issues affecting other systems.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →