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Engine-Codes – GMC – P0878 2017 GMC Sierra

P0878 2017 GMC Sierra Code - Transmission Fluid Pressure Switch 4 Circuit High Voltage

Quick Answer

The P0878 diagnostic trouble code (DTC) for a 2017 GMC Sierra indicates an issue with the Transmission Fluid Pressure Switch 4 Circuit High Voltage. Common causes include Faulty transmission fluid pressure switch, Short circuit in the wiring harness, Open circuit in the wiring. 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 2017 GMC Sierra indicates Transmission Fluid Pressure Switch 4 Circuit High Voltage.
Common causes
Common causes include Faulty transmission fluid pressure switch, Short circuit in the wiring harness, Open circuit in the wiring.
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 12, 2024
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Code P0878 2017 GMC Sierra Description

The P0878 diagnostic trouble code (DTC) for a 2017 GMC Sierra indicates an issue with the Transmission Fluid Pressure Switch 4 Circuit High Voltage. This code specifically points to a problem with the transmission fluid pressure switch, which is responsible for monitoring the hydraulic pressure within the transmission system. The switch is designed to send signals to the vehicle's engine control module (ECM) to ensure proper shifting and overall transmission performance.

OBDII Code P0878 2017 GMC Sierra - Transmission Fluid Pressure Switch 4 Circuit High Voltage
P0878 2017 GMC Sierra Code - Transmission Fluid Pressure Switch 4 Circuit High Voltage

Common Causes of P0878 2017 GMC Sierra

  1. Faulty transmission fluid pressure switch
  2. Short circuit in the wiring harness
  3. Open circuit in the wiring
  4. Corrosion or poor connection in the electrical system
  5. ECM malfunction

Symptoms of P0878 2017 GMC Sierra

  1. Harsh shifting between gears
  2. Delayed engagement when shifting
  3. Slipping gears during acceleration
  4. Transmission overheating
  5. Vehicle going into failsafe mode

How to Fix P0878 2017 GMC Sierra

  1. Begin by using a diagnostic scanner to confirm the P0878 code and pinpoint the exact cause of the issue.
  2. Inspect the wiring harness connected to the transmission fluid pressure switch for any signs of damage, corrosion, or loose connections. Repair or replace as necessary.
  3. Test the transmission fluid pressure switch using a multimeter to determine if it is functioning correctly. Replace the switch if it is faulty.
  4. Clear the DTC from the ECM memory using the diagnostic scanner and perform a test drive to ensure the issue has been resolved.
  5. If the problem persists, further diagnostics may be required to identify any underlying issues with the transmission system.

Cost to Fix P0878 2017 GMC Sierra

The typical repair costs for addressing a P0878 code on a 2017 GMC Sierra can vary depending on the specific cause of the issue. In general, replacing a faulty transmission fluid pressure switch can cost between $100 and $300, including parts and labor. However, if the problem is related to wiring issues or an ECM malfunction, the repair costs may increase. It's recommended to consult with a professional mechanic to get an accurate estimate based on the specific diagnosis and repair needed. Keep in mind that labor rates at auto repair shops can vary, so it's advisable to inquire about local rates for a more precise cost 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 2017 GMC Sierra Code

1. What does the OBDII code P0878 mean on a 2017 GMC Sierra?

P0878 indicates that the Transmission Control Module (TCM) has detected high voltage in the Transmission Fluid Pressure Switch 4 circuit, which monitors hydraulic pressure in the transmission.

2. What are the common symptoms of code P0878 on a 2017 GMC Sierra?

Symptoms may include erratic shifting, the transmission stuck in one gear, delayed engagement, limp mode activation, and the check engine light being illuminated.

3. What causes the P0878 code to appear on a 2017 GMC Sierra?

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

4. Can low transmission fluid cause the P0878 code on a 2017 GMC Sierra?

Yes, low or dirty transmission fluid can lead to improper hydraulic pressure, which may trigger the P0878 code.

5. How do you diagnose the P0878 code on a 2017 GMC Sierra?

Diagnosis typically involves using an OBDII scanner, checking transmission fluid levels and condition, inspecting the wiring and connectors for damage, and testing the transmission fluid pressure switch.

6. Can you drive a 2017 GMC Sierra with a P0878 code?

Driving with the P0878 code is not recommended as it can lead to transmission damage or unsafe driving conditions due to erratic shifting or limp mode.

7. How do you fix the P0878 code on a 2017 GMC Sierra?

Repairs may involve replacing the transmission fluid pressure switch, repairing or replacing damaged wiring, cleaning or replacing the transmission fluid, or reprogramming or replacing the TCM.

8. How much does it cost to repair the P0878 code on a 2017 GMC Sierra?

Repair costs can vary, but replacing a transmission fluid pressure switch typically ranges from $150 to $300, while wiring repairs or TCM replacement can be more expensive.

9. Can a faulty TCM cause the P0878 code in a 2017 GMC Sierra?

Yes, a malfunctioning Transmission Control Module can cause incorrect voltage readings in the Transmission Fluid Pressure Switch 4 circuit, leading to the P0878 code.

10. What tools are needed to troubleshoot the P0878 code on a 2017 GMC Sierra?

You’ll need an OBDII scanner, a multimeter for testing electrical connections, and potentially a transmission pressure gauge to verify hydraulic pressure.

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