AutoCodes – GMC – P0179 GMC

P0179 GMC Code - Fuel Composition Sensor Circuit High Frequency

Quick Answer

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. Common causes include Faulty Fuel Composition Sensor (FCS) or Flex Fuel Sensor, Fuel Composition Sensor harness is open or shorted, Fuel Composition Sensor circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0179 GMC indicates Fuel Composition Sensor Circuit High Frequency.
Common causes: Common causes include Faulty Fuel Composition Sensor (FCS) or Flex Fuel Sensor, Fuel Composition Sensor harness is open or shorted, Fuel Composition Sensor circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 829

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

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Table of contents Created and updated by William Orellana on May 29, 2022

Description
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
FAQs
Comments
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Code P0179 GMC Description

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.

OBDII Code P0179 GMC - Fuel Composition Sensor Circuit High Frequency - AutoCodes.com — P0179 GMC Code - Fuel Composition Sensor Circuit High Frequency

What does this mean?

What are the Possible Causes of the DTC P0179 GMC?

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)

How to Fix the DTC P0179 GMC?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

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

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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0179 GMC code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0179 GMC code?

Need more information on how to fix the P0179 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0179 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P0179 2014 GMC Sierra — Fuel Composition Sensor Circuit High Frequency
P0179 2015 GMC Sierra — Fuel Composition Sensor Circuit High Frequency
P0179 2016 GMC Sierra — Fuel Composition Sensor Circuit High Frequency
P0179 2017 GMC Sierra — Fuel Composition Sensor Circuit High Frequency
P0179 2018 GMC Sierra — Fuel Composition Sensor Circuit High Frequency

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0179 GMC Code

1. What are the common symptoms of OBDII code P0179 GMC?

The common symptoms of OBDII code P0179 GMC include rough idling, decreased fuel efficiency, engine stalling, and a noticeable decrease in engine performance.

2. What does the OBDII code P0179 GMC indicate?

OBDII code P0179 GMC indicates an issue with the Fuel Composition Sensor Circuit High Frequency. This means that the fuel composition sensor is detecting a high frequency signal, which can lead to improper fuel mixture in the engine.

3. What are the potential causes of OBDII code P0179 GMC?

Some potential causes of OBDII code P0179 GMC include a faulty fuel composition sensor, wiring issues in the sensor circuit, a poor electrical connection, or a problem with the engine control module.

4. How can I diagnose the OBDII code P0179 GMC?

Diagnosing OBDII code P0179 GMC may involve using an OBDII scanner to retrieve the code and checking the fuel composition sensor for any visible damage. Additionally, inspecting the wiring and connections related to the sensor can help identify the issue.

5. What are the repair options for OBDII code P0179 GMC?

Repair options for OBDII code P0179 GMC may include replacing the fuel composition sensor, repairing any damaged wiring or connections, and resetting the trouble code using an OBDII scanner.

6. Can OBDII code P0179 GMC cause damage to the engine?

While OBDII code P0179 GMC itself may not cause direct damage to the engine, it can lead to poor engine performance and fuel efficiency if left unresolved. It is recommended to address the issue promptly to avoid potential complications.

7. Is it safe to continue driving with OBDII code P0179 GMC?

It is not recommended to continue driving with OBDII code P0179 GMC, as it can impact the engine's performance and fuel efficiency. It is advisable to address the issue as soon as possible to prevent further damage.

8. How much does it typically cost to repair OBDII code P0179 GMC?

The cost of repairing OBDII code P0179 GMC can vary depending on the specific cause of the issue, the labor rates in your area, and the cost of replacement parts. It is advisable to consult a mechanic for an accurate estimate.

9. Can I reset OBDII code P0179 GMC on my own?

You can reset OBDII code P0179 GMC on your own using an OBDII scanner. However, it is important to address the underlying issue causing the trouble code to prevent it from reoccurring.

10. How can I prevent OBDII code P0179 GMC from appearing again?

To prevent OBDII code P0179 GMC from appearing again, it is essential to perform regular maintenance on your vehicle, including checking the fuel composition sensor and related components for any signs of wear or damage.