AutoCodes – GMC – U0078 2017 GMC Sierra

U0078 2017 GMC Sierra Code - Control Module Communication Low Speed CAN Bus Off

Quick Answer

The low-speed General Motor Local Area Network (GMLAN) serial data bus is used to communicate information between the devices. Common causes include Check for more codes, Faulty Control Module, Control Module harness is open or shorted. 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: U0078 2017 GMC Sierra indicates Control Module Communication Low Speed CAN Bus Off.
Common causes: Common causes include Check for more codes, Faulty Control Module, Control Module harness is open or shorted.
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 312

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 Jul 20, 2023

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U0078 2017 GMC Sierra Description

The low-speed General Motor Local Area Network (GMLAN) serial data bus is used to communicate information between the devices. The serial data is transmitted over a single wire to the appropriate devices. The low-speed GMLAN serial data circuits also connect directly to the Data Link Connector (DLC). The Diagnostic Trouble Code (DTC) sets when the device setting the DTC has attempted to establish communications on the serial data circuits more than 3 times in 5 s.

OBDII Code U0078 2017 GMC Sierra - Control Module Communication Low Speed CAN Bus Off - AutoCodes.com — U0078 2017 GMC Sierra Code - Control Module Communication Low Speed CAN Bus Off

What does this mean?

What are the Possible Causes of the DTC U0078 2017 GMC Sierra?

Check for more codes
Faulty Control Module
Control Module harness is open or shorted
Control Module circuit poor electrical connection

How to Fix the DTC U0078 2017 GMC Sierra?

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 U0078 2017 GMC Sierra 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 U0078 2017 GMC Sierra code?

Need more information on how to fix the U0078 2017 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

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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 U0078 2017 GMC Sierra Code

1. What does the OBDII code U0078 mean on a 2017 GMC Sierra?

The U0078 code indicates an issue with the Low-Speed CAN (Controller Area Network) Bus, specifically a communication fault or disconnection between control modules.

2. What are the common symptoms of the U0078 code?

Symptoms may include warning lights on the dashboard, such as the check engine light, loss of communication with certain vehicle systems, or improper functioning of features like the infotainment system or climate control.

3. What causes the U0078 code to appear?

The most common causes include damaged wiring, faulty connectors, a malfunctioning module on the Low-Speed CAN Bus, or a short circuit in the communication network.

4. Can I drive my 2017 GMC Sierra with the U0078 code?

While the vehicle may still be drivable, certain systems may not function correctly, which could lead to safety concerns. Itâ€™s best to diagnose and repair the issue promptly.

5. How do you diagnose the U0078 code on a GMC Sierra?

Diagnosis typically involves using a scan tool to check for related codes, inspecting wiring and connectors in the Low-Speed CAN Bus network, and testing individual modules for proper operation.

6. Is the U0078 code specific to the 2017 GMC Sierra?

No, the U0078 code can appear in other vehicles as well, but the specific systems and modules affected may vary depending on the make and model.

7. What repairs are commonly needed to fix the U0078 code?

Repairs may include replacing damaged wiring, fixing or replacing faulty connectors, or replacing a malfunctioning control module on the Low-Speed CAN Bus.

8. How much does it cost to fix the U0078 code on a 2017 GMC Sierra?

Repair costs can vary widely depending on the root cause, but fixing wiring or connectors typically costs less than replacing a faulty control module, which could range from $150 to $1,000 or more.

9. Can a software update fix the U0078 code?

In some cases, a software update for one or more control modules may resolve communication issues, but physical problems like wiring damage will require repairs.

10. What tools are needed to troubleshoot the U0078 code?

A professional-grade OBDII scanner with CAN Bus diagnostic capabilities, a multimeter for testing electrical circuits, and wiring diagrams for the 2017 GMC Sierra are essential for troubleshooting.