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Engine-Codes – GMC – P077C GMC

P077C GMC Code - Transmission Output Speed Sensor Circuit Low Voltage

Quick Answer

The P077C GMC code indicates a problem with the transmission output speed sensor circuit, specifically a low voltage issue. Common causes include Faulty transmission output speed sensor, Damaged wiring or connectors in the sensor circuit, Malfunctioning transmission control module. 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
P077C GMC indicates Transmission Output Speed Sensor Circuit Low Voltage.
Common causes
Common causes include Faulty transmission output speed sensor, Damaged wiring or connectors in the sensor circuit, Malfunctioning transmission control module.
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.
What is this?
Table of contents Created and updated by William Orellana on Sep 23, 2024
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Code P077C GMC Description

The P077C GMC code indicates a problem with the transmission output speed sensor circuit, specifically a low voltage issue. The transmission output speed sensor is responsible for monitoring the speed of the output shaft of the transmission. This information is crucial for the transmission control module to determine the appropriate shift points and ensure smooth operation of the transmission.

OBDII Code P077C GMC - Transmission Output Speed Sensor Circuit Low Voltage
P077C GMC Code - Transmission Output Speed Sensor Circuit Low Voltage

Common Causes of P077C GMC

  1. Faulty transmission output speed sensor
  2. Damaged wiring or connectors in the sensor circuit
  3. Malfunctioning transmission control module
  4. Power supply issues to the sensor
  5. Corrosion or contamination in the sensor connections

Symptoms of P077C GMC

  1. Harsh or delayed shifting
  2. Transmission slipping
  3. Illuminated check engine light
  4. Limp mode activation
  5. Decreased fuel efficiency

How to Fix P077C GMC

  1. Begin by diagnosing the specific cause of the low voltage issue by testing the transmission output speed sensor, wiring, connectors, and the transmission control module.
  2. Replace the faulty transmission output speed sensor if it is found to be the cause of the low voltage.
  3. Repair or replace any damaged wiring or connectors in the sensor circuit.
  4. Check and repair any power supply issues to the sensor.
  5. Clear the diagnostic trouble codes and test drive the vehicle to ensure the issue has been resolved.

Cost to Fix P077C GMC

The cost of repairing a transmission output speed sensor circuit low voltage issue can vary depending on the specific cause of the problem and the labor rates in your area. On average, the cost of replacing a transmission output speed sensor ranges from $100 to $300, including parts and labor. Additional costs may be incurred if there are wiring or connector issues that need to be addressed. It's recommended to consult with a professional mechanic to get an accurate estimate based on your vehicle's make and model. Labor rates at auto repair shops typically range from $80 to $150 per hour, but can vary based on location and other factors.

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Information for Specific GMC Models

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 P077C GMC Code

1. What does the OBDII code P077C mean for a GMC vehicle?

P077C indicates a low voltage issue in the transmission output speed sensor circuit, which monitors the rotational speed of the transmission output shaft.

2. What are the common symptoms of code P077C in a GMC?

Symptoms may include erratic shifting, transmission slipping, reduced fuel efficiency, a lit check engine light, or the transmission entering limp mode.

3. What causes the P077C code to appear?

The code can be triggered by a faulty output speed sensor, damaged wiring or connectors in the circuit, low transmission fluid, or an issue with the powertrain control module (PCM).

4. Can driving with the P077C code damage my GMC's transmission?

Yes, continued driving with this code can lead to further transmission issues or damage due to improper shifting or slipping.

5. How do I diagnose the P077C code on my GMC?

Start by inspecting the wiring and connectors for damage or corrosion, check the output speed sensor for proper operation, and ensure the transmission fluid level is correct.

6. How do I fix the P077C code in a GMC vehicle?

Repairs may involve replacing the output speed sensor, repairing or replacing damaged wiring, cleaning corroded connectors, or reprogramming the PCM if necessary.

7. How much does it cost to fix a P077C code on a GMC?

Costs vary depending on the issue. Replacing an output speed sensor typically costs $100–$300, while addressing wiring or PCM issues may cost more.

8. Can low transmission fluid cause the P077C code in a GMC?

Yes, low or contaminated transmission fluid can interfere with sensor operation and trigger this code.

9. Is the P077C code specific to GMC vehicles?

No, while it can appear in GMC vehicles, the P077C code is a generic OBDII code and may also occur in other makes and models.

10. Do I need professional help to repair the P077C code on my GMC?

If you're comfortable inspecting wiring and replacing sensors, you may be able to fix it yourself. Otherwise, seek help from a qualified mechanic.

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