P0177Fuel Composition Sensor Circuit Range/Performance
- 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. P0177 means the signal lies within the valid frequency range but is implausible – it jumps, changes without a refuelling event or does not match the mixture adaptation. Such sensors measure permittivity, conductivity and temperature and compare them with tables of known blends. GM's documents only list low, high and P2269, so no manufacturer threshold for P0177 was found; the description rests on CARB's rationality requirement and component information.
- What you may notice
- Check engine light on
- Wrong ethanol value, stumbling or starting problems
- Adaptation codes P0171/P0172
- Likely causes
- LikelySensor drifting or dirty inside
- PossibleWater or contamination in the fuel
- PossibleLoose contact in the connector
- RareControl module or software
- 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.