Engine-Codes - Generic - P0179

P0179 Code - Fuel Composition Sensor Circuit High Frequency

- Code Popularity: 30,889 Views
- Repair Importance Level: 3/3
- Repair Difficulty Level: 3/3
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What are the Possible Causes of the DTC P0179?

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
  • Faulty Fuel Composition Sensor (FCS) or Flex Fuel Sensor
  • Fuel Composition Sensor harness is open or shorted
  • Fuel Composition Sensor circuit poor electrical connection
  • Faulty Engine Control Module (ECM)

Code Tech Notes

Replacing the Fuel Composition Sensor (FCS) or Flex Fuel Sensor usually takes care of the code.





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How to Fix the DTC P0179?

Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

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What is the Cost to Diagnose the Code?

Labor: 1.0

The cost to diagnose the P0179 code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.

What are Code Possible Symptoms?

  • Engine Light ON (or Service Engine Soon Warning Light)

What Does the P0179 Code Mean?

The Fuel Composition Sensor (FCS), or Flex Fuel Sensor (service parts term), measures the ethanol-gasoline ratio of the fuel being used in a flexible fuel vehicle. Flexible fuel vehicles can be operated with a blend of up to 85 percent ethanol. To adjust the ignition timing and the air to fuel ratio, the engine management system requires information about the percentage of ethanol in the fuel.
Alcohol content information is supplied to the Engine Control Module (ECM) from the Fuel Composition Sensor. The Fuel Composition Sensor has an ignition positive circuit, a signal circuit, and a ground circuit. The Fuel Composition Sensor uses a microprocessor inside the sensor to measure the ethanol percentage and changes the output signal accordingly. The signal circuit carries the ethanol percentage via the frequency signal. The ECM provides an internal pull up to 5V on the signal circuit, and the fuel composition sensor pulls the 5V to ground in pulses. The normal range of operating frequency is between 50 - 150 Hz. The microprocessor inside the sensor is capable of a certain amount of self-diagnosis. An output frequency between 180 Hz and 190 Hz indicates that the fuel is contaminated. The Diagnostic Trouble Code (DTC) will be set when the ECM detects that the fuel composition sensor output frequency is less than 45 Hz for greater than 6s.

P0179 Code - Fuel Composition Sensor Circuit High Frequency

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Code P0179 Information for Specific Makes

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