P0179Fuel Composition Sensor Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The fuel composition sensor is fitted only to flex-fuel vehicles that can run on petrol or ethanol up to E85. GM uses a capacitive sensor in the fuel line whose square-wave output frequency gives the ethanol content – 50 Hz for E0 up to 150 Hz for E100 – while the pulse width carries the fuel temperature. Ford has calculated the ethanol content from the oxygen sensor feedback after refuelling since model year 2000 and has no such sensor. P0179 means the frequency is above the physically possible range for E100 plus tolerance. GM sets it between 155 and 185 Hz (50 of 63 samples, two trips); above 185 Hz it sets P2269 instead, because such a high value indicates water or conductive fuel rather than a sensor fault. Typical causes of P0179 are failed sensor electronics or interference on the signal wire. With a falsely high ethanol value the mixture tends to run rich.
- What you may notice
- Check engine light on
- Ethanol value implausibly high (100 %)
- Rich mixture, stumbling, higher consumption
- Likely causes
- LikelySensor electronics faulty
- PossibleInterference or short on the signal wire
- PossibleWater or conductive fuel near the P2269 limit
- RareEngine control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €80 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.