P0177 — Fuel Composition Sensor Circuit Range / Performance
The flex-fuel composition sensor signal is within electrical limits but does not match expected values for the current fuel mix or rate-of-change is implausible.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Flex fuel composition sensor
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Sensor drifted out of calibration
- Fuel contaminated (water, dirt)
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.