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P0178 - Fuel Composition Sensor Circuit Low Input

Possible causes
- Flexible Fuel (FF) sensor to Vehicle Power (VPWR) circuit harness open or shorted
- FF to VPWR circuit poor electrical connection
- Open in FF sensor signal circuit
- Short to ground in FF sensor signal circuit
- Fuel contamination
- Short to VPWR in FF sensor batte
What does this mean? What does this mean?
Tech notes
Replaced Fuel Composition Sensor
What does this mean? What does this mean?
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P0178 Description

Fuel Composition Sensors are used to determine the amount of ethanol alcohol in the gasoline. Normally, a gasoline engine should not have more than 10% ethanol alcohol in the fuel for proper operation. Some vehicles have a Flexible Fuel (FF) system on them that allow them to run on up to 85% ethanol alcohol in the fuel. The fuel composition sensor sends a frequency modulated signal to the engine controller which is proportional to the alcohol content of the fuel. The injector pulse width and the ignition timing are modified for the increased alcohol content. It takes almost twice the amount of alcohol compared to gasoline to produce the same power.

P0178 Information for specific makes
P0178 BUICK Fuel Composition Sensor Circuit Low Frequency
P0178 CHEVROLET Fuel Composition Sensor Circuit Low Frequency
P0178 GMC Fuel Composition Sensor Circuit Low Frequency
P0178 MERCEDES-BENZ Fuel Composition Sensor Circuit Low Input
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