AutoCodes – GMC – U0078 2018 GMC Sierra

U0078 2018 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 2018 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 347

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 2018 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 2018 GMC Sierra - Control Module Communication Low Speed CAN Bus Off - AutoCodes.com — U0078 2018 GMC Sierra Code - Control Module Communication Low Speed CAN Bus Off

What does this mean?

What are the Possible Causes of the DTC U0078 2018 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 2018 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 2018 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 2018 GMC Sierra code?

Need more information on how to fix the U0078 2018 GMC Sierra code? Get Access to Factory Service Manuals

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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 2018 GMC Sierra Code

1. What does the OBDII code U0078 mean on a 2018 GMC Sierra?

The U0078 code indicates a communication fault on the low-speed CAN (Controller Area Network) bus, specifically that a control module has gone offline or lost communication.

2. What are the common symptoms of the U0078 code in a 2018 GMC Sierra?

Symptoms may include warning lights on the dashboard, malfunctioning electrical systems (e.g., windows or locks), failure of certain control modules to respond, or intermittent communication errors.

3. What causes the U0078 code in a 2018 GMC Sierra?

Common causes include damaged or corroded wiring, loose connectors, a malfunctioning control module, or interference from an aftermarket accessory improperly installed.

4. Is the U0078 code serious and can I still drive my 2018 GMC Sierra?

While the vehicle may still be drivable, the code indicates a network communication issue that could affect critical functions. It is recommended to address it promptly to avoid further complications.

5. How do I diagnose the U0078 code on a 2018 GMC Sierra?

Start by checking the wiring and connectors on the low-speed CAN bus for damage or corrosion. Use a scan tool to verify which modules are not communicating and inspect the low-speed CAN circuit.

6. Can a dead battery cause the U0078 code on a 2018 GMC Sierra?

Yes, a dead or weak battery can cause communication errors, including the U0078 code, as low voltage can disrupt the CAN bus network.

7. How do I fix the U0078 code in my 2018 GMC Sierra?

Repairs may include repairing or replacing damaged wiring, cleaning or securing loose connectors, replacing a faulty control module, or reprogramming affected modules.

8. Can aftermarket accessories trigger the U0078 code on a 2018 GMC Sierra?

Yes, improperly installed aftermarket accessories, such as stereos or lighting systems, can interfere with the low-speed CAN bus and cause this code.

9. Does the U0078 code require module reprogramming in a 2018 GMC Sierra?

In some cases, module reprogramming may be needed if the issue stems from software corruption or if a control module has been replaced.

10. How much does it cost to repair the U0078 code on a 2018 GMC Sierra?

The cost depends on the cause. Simple wiring or connector repairs may cost $100â€“$300, while replacing a control module could cost $500 or more, including programming.