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DTC codes / P01xx · Fuel and air metering / P0178

P0178Fuel Composition Sensor Circuit Low

P0178 means the powertrain control module (PCM) has detected a fuel composition sensor signal voltage that is lower than the expected range for the current operating conditions. The sensor, typically a flex-fuel sensor on vehicles designed to run on ethanol blends, reports the ethanol content and temperature of the fuel, and a low signal indicates either a circuit fault or an internal sensor failure.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage