AutoCodes – GMC – P0878 GMC

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

Quick Answer

The Transmission Fluid Pressure (TFP) switch 4 is part of the Transmission Control Solenoid Valve Assembly which has no serviceable parts. Common causes include Low transmission fluid level, Dirty transmission fluid, Faulty Transmission Control Solenoid Valve Assembly. 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 GMC indicates Transmission Fluid Pressure Switch 4 Circuit High Voltage.
Common causes: Common causes include Low transmission fluid level, Dirty transmission fluid, Faulty Transmission Control Solenoid Valve Assembly.
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 808

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 03, 2022

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0878 GMC Description

The Transmission Fluid Pressure (TFP) switch 4 is part of the Transmission Control Solenoid Valve Assembly which has no serviceable parts. The Transmission Control Module (TCM) supplies a signal circuit to the TFP switch 4. The TFP switch 4 has an internal case ground. TFP switch 4 is normally closed or LOW. When oil pressure is present at the TFP switch 4, the switch is open or HIGH. The normal LOW pressure control solenoid 5 controls pressure to the 1-2-3-4 clutch regulator valve. The TCM monitors the TFP switch 4 to determine the position of the 1-2-3-4 clutch regulator valve. When the 1-2-3-4 clutch is commanded OFF, pressure is present on the TFP switch 4. When the 1-2-3-4 clutch is commanded ON, the 1-2-3-4 clutch regulator valve moves and pressure to the TFP switch 4 is exhausted through the 1-2-3-4 clutch regulator valve. The Diagnostic Trouble Code (DTC) will be set when the TCM detects that the TFP switch 4 signal voltage remains HIGH after the 1-2-3-4 clutch transitions from a LOW pressure state to a HIGH pressure state. The TCM counts each incident. The DTC sets when 8 counts are accumulated.

OBDII Code P0878 GMC - Transmission Fluid Pressure Switch 4 Circuit High Voltage - AutoCodes.com — P0878 GMC Code - Transmission Fluid Pressure Switch 4 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P0878 GMC?

Low transmission fluid level
Dirty transmission fluid
Faulty Transmission Control Solenoid Valve Assembly
Transmission Control Solenoid Valve Assembly harness is open or shorted
Transmission Control Solenoid Valve Assembly circuit poor electrical connection

How to Fix the DTC P0878 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 is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0878 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 P0878 GMC code?

Need more information on how to fix the P0878 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0878 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P0878 2014 GMC Sierra — Transmission Fluid Pressure Switch 4 Circuit High Voltage
P0878 2015 GMC Sierra — Transmission Fluid Pressure Switch 4 Circuit High Voltage
P0878 2016 GMC Sierra — Transmission Fluid Pressure Switch 4 Circuit High Voltage
P0878 2017 GMC Sierra — Transmission Fluid Pressure Switch 4 Circuit High Voltage
P0878 2018 GMC Sierra — Transmission Fluid Pressure Switch 4 Circuit High Voltage

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 GMC Code

1. What are the common symptoms of OBDII code P0878 on a GMC vehicle?

The common symptoms of OBDII code P0878 include harsh shifting, erratic transmission behavior, transmission slippage, and illuminated warning lights on the dashboard.

2. What does the OBDII code P0878 on a GMC indicate?

OBDII code P0878 indicates a high voltage condition in Transmission Fluid Pressure Switch 4 Circuit, signaling a potential issue with the transmission fluid pressure control system.

3. What are the possible causes of OBDII code P0878 in a GMC vehicle?

Possible causes of OBDII code P0878 include a faulty transmission fluid pressure switch, wiring or connector issues, low transmission fluid level, or a malfunctioning transmission control module.

4. How can I diagnose the source of OBDII code P0878 on my GMC vehicle?

Diagnosing OBDII code P0878 involves checking the transmission fluid level, inspecting the wiring and connectors related to the pressure switch, and using a scan tool to monitor the switch's voltage readings.

5. Can I continue driving my GMC vehicle with OBDII code P0878 present?

It is not recommended to continue driving your GMC vehicle with OBDII code P0878 present, as it can lead to further damage to the transmission components and potentially result in more costly repairs.

6. How can I repair OBDII code P0878 in my GMC vehicle?

Repairing OBDII code P0878 may involve replacing the Transmission Fluid Pressure Switch 4 Circuit, repairing any damaged wiring or connectors, ensuring the correct transmission fluid level, and clearing the trouble code.

7. Is it possible to reset OBDII code P0878 on a GMC without fixing the underlying issue?

While it is possible to clear the trouble code temporarily, OBDII code P0878 will likely reappear if the root cause of the high voltage condition in the transmission fluid pressure switch is not addressed.

8. Can a DIY enthusiast fix OBDII code P0878 on a GMC, or is professional assistance required?

Depending on the individual's skill level and access to tools, a DIY enthusiast may be able to address OBDII code P0878 by following repair guides and utilizing proper diagnostic equipment. However, professional assistance is recommended for complex transmission-related issues.

9. How much does it typically cost to repair OBDII code P0878 in a GMC vehicle?

The cost of repairing OBDII code P0878 can vary based on the extent of the damage and the specific components needing replacement. Costs may range from a few hundred dollars for simple repairs to over a thousand dollars for more extensive transmission work.

10. Are there any preventive maintenance measures to help avoid OBDII code P0878 in a GMC vehicle?

Regularly checking and maintaining the transmission fluid level, addressing any leaks promptly, and ensuring the transmission system is serviced according to the manufacturer's recommendations can help prevent issues like OBDII code P0878 from occurring.