P0179 Fuel Composition Sensor Circuit High

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.

Likely causes

Symptoms

• Check engine light on
• Ethanol value implausibly high (100 %)
• Rich mixture, stumbling, higher consumption

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.