P CODES (POWERTRAIN) P0100 - P0199 P0179

    A Comprehensive Guide to Understanding, Diagnosing, and Repairing Trouble Code P0179: Fuel Composition Sensor Circuit High Input

    Definition of Trouble Code P0179 - Fuel Composition Sensor Circuit High Input

    The P0179 trouble code is related to the fuel composition sensor circuit, specifically indicating a high input signal. The fuel composition sensor is responsible for determining the ethanol content in vehicles that use flex-fuel or E85 fuel. The engine control module (ECM) adjusts the fuel mixture and ignition timing based on the ethanol percentage detected. A high input signal signifies that the sensor is sending incorrect or excessively high voltage to the ECM, which may lead to poor engine performance or increased emissions.

    Diagnosing Trouble Code P0179

    Before beginning the diagnostic process for code P0179, you should gather the necessary tools and materials, such as a digital multimeter, a scan tool, a repair manual specific to your vehicle, and safety equipment.

    Step 1: Retrieve stored codes and data

    Use the scan tool to check for any stored codes and freeze frame data. This information will help you understand the conditions when the code was set and may help in diagnosing the problem.

    Step 2: Inspect the fuel composition sensor and its wiring

    Locate the fuel composition sensor in your vehicle, typically near the fuel line. Visually inspect the sensor and its wiring for any signs of damage, corrosion, or loose connections. If any issues are found, repair or replace the damaged components as necessary.

    Step 3: Test the fuel composition sensor

    Consult your vehicle's repair manual to identify the correct pins on the sensor connector. Using a digital multimeter, check the resistance between the specified pins. Compare the readings to the specifications listed in the repair manual. If the readings are not within the specified range, replace the fuel composition sensor.

    Step 4: Test the wiring and circuitry

    If the sensor is functioning properly, the issue may lie in the wiring or circuitry. Check the wiring for continuity, and ensure that the wiring is securely connected to the ECM. If any wiring issues are found, repair or replace as needed. Additionally, check the ECM for any signs of damage or malfunction.

    Repairing Trouble Code P0179

    Step 1: Replace the fuel composition sensor (if necessary)

    If the diagnostic process determined that the fuel composition sensor is faulty, replace it with a new one. Be sure to follow the manufacturer's recommended procedures for installation.

    Step 2: Repair or replace damaged wiring or components

    If any damaged wiring, connectors, or components were found during the diagnostic process, repair or replace them as necessary. Ensure that all connections are secure and free from corrosion.

    Step 3: Clear stored codes and test drive

    After completing the necessary repairs, clear the stored codes using the scan tool. Then, take the vehicle for a test drive under similar conditions to those when the code was set. Monitor the scan tool to ensure that the code does not reappear.


    Trouble code P0179 - Fuel Composition Sensor Circuit High Input can lead to poor engine performance and increased emissions. Diagnosing and repairing the issue may involve inspecting the fuel composition sensor, its wiring, and associated circuitry. Always follow the manufacturer's recommended procedures and specifications when diagnosing and repairing this code.

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