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P0878 2014 GMC Sierra Code - Transmission Fluid Pressure Switch 4 Circuit High Voltage

Quick Answer

The P0878 diagnostic trouble code (DTC) for a 2014 GMC Sierra indicates that there is a high voltage condition detected in the transmission fluid pressure switch 4 circuit. Common causes include Faulty transmission fluid pressure switch, Wiring or connector issues in the circuit, Transmission control module malfunction. 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
P0878 2014 GMC Sierra indicates Transmission Fluid Pressure Switch 4 Circuit High Voltage.
Common causes
Common causes include Faulty transmission fluid pressure switch, Wiring or connector issues in the circuit, Transmission control module malfunction.
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 16, 2024
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Code P0878 2014 GMC Sierra Description

The P0878 diagnostic trouble code (DTC) for a 2014 GMC Sierra indicates that there is a high voltage condition detected in the transmission fluid pressure switch 4 circuit. This switch is responsible for monitoring the hydraulic pressure within the transmission system and sending signals to the vehicle's computer to regulate shifting and other transmission functions. When the voltage in this circuit is higher than normal, it can lead to issues with the transmission's performance and overall drivability of the vehicle.

OBDII Code P0878 2014 GMC Sierra - Transmission Fluid Pressure Switch 4 Circuit High Voltage
P0878 2014 GMC Sierra Code - Transmission Fluid Pressure Switch 4 Circuit High Voltage

Common Causes of P0878 2014 GMC Sierra

  1. Faulty transmission fluid pressure switch
  2. Wiring or connector issues in the circuit
  3. Transmission control module malfunction
  4. Low transmission fluid levels
  5. Contaminated or degraded transmission fluid

Symptoms of P0878 2014 GMC Sierra

  1. Harsh or delayed shifting
  2. Erratic transmission behavior
  3. Transmission slippage
  4. Illuminated Check Engine Light
  5. Reduced fuel efficiency

How to Fix P0878 2014 GMC Sierra

  1. Begin by diagnosing the specific cause of the high voltage condition, using a scan tool to retrieve the DTC and checking the transmission fluid level and condition.
  2. Inspect the wiring and connectors in the transmission fluid pressure switch 4 circuit for any damage or corrosion, repairing or replacing as needed.
  3. Test the transmission fluid pressure switch for proper operation and replace it if it is found to be faulty.
  4. Clear the DTC from the vehicle's computer memory and test drive the vehicle to ensure that the issue has been resolved.
  5. Perform a transmission fluid flush and refill if necessary, to ensure proper fluid levels and quality.

Cost to Fix P0878 2014 GMC Sierra

The typical repair costs for addressing a P0878 code in a 2014 GMC Sierra can range from $200 to $500, depending on the specific cause of the issue and the cost of parts and labor. It's important to note that diagnosis time and labor rates at auto repair shops can vary, so it's advisable to check with local shops for a more accurate estimate.

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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 P0878 2014 GMC Sierra Code

1. What does the OBDII code P0878 mean on a 2014 GMC Sierra?

P0878 indicates a "Transmission Fluid Pressure Switch 4 Circuit High Voltage," meaning the transmission control module (TCM) has detected an abnormally high voltage signal from the transmission fluid pressure sensor for circuit 4.

2. What are the common symptoms of code P0878 in a 2014 GMC Sierra?

Symptoms may include harsh or delayed shifting, slipping gears, the transmission being stuck in one gear (limp mode), illuminated check engine light, and reduced fuel efficiency.

3. What causes the P0878 code to appear in my GMC Sierra?

Common causes include a faulty transmission fluid pressure sensor, damaged or corroded wiring or connectors in the circuit, a malfunctioning TCM, or low or contaminated transmission fluid.

4. Can low transmission fluid cause the P0878 code?

Yes, low or contaminated transmission fluid can affect the pressure sensor readings and trigger the P0878 code.

5. How do I diagnose the P0878 code on my 2014 GMC Sierra?

Start by inspecting the transmission fluid level and condition, checking for damaged wiring or connectors in the pressure switch circuit, and testing the transmission fluid pressure sensor with a multimeter.

6. Is it safe to drive with the P0878 code on my GMC Sierra?

Driving with this code is not recommended, as it may lead to poor transmission performance, additional damage, or unsafe driving conditions.

7. How do I fix the P0878 code on a 2014 GMC Sierra?

Repairs may include replacing the transmission fluid pressure sensor, repairing or replacing damaged wiring, cleaning corroded connectors, or reprogramming or replacing the TCM if necessary.

8. How much does it cost to repair the P0878 code on a GMC Sierra?

The cost varies depending on the issue. Replacing a transmission fluid pressure sensor typically costs $150–$300, while more extensive TCM repairs or wiring fixes can cost more.

9. Can a bad transmission control module (TCM) cause the P0878 code?

Yes, a malfunctioning TCM can send or interpret incorrect signals from the pressure sensor circuit, leading to the P0878 code.

10. Will resetting the code fix the P0878 issue on my GMC Sierra?

Clearing the code without addressing the underlying issue will not fix the problem, and the code is likely to return. Proper diagnosis and repair are necessary for a permanent solution.

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