AutoCodes – GMC – U18C8 2015 GMC Sierra

U18C8 2015 GMC Sierra Code - Glow Plug Control Module Lost Communication with Engine Control Module

Quick Answer

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Common causes include Faulty Engine Control Module (ECM), Engine Control Module harness is open or shorted, Engine Control Module circuit poor electrical connection. 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: U18C8 2015 GMC Sierra indicates Glow Plug Control Module Lost Communication with Engine Control Module.
Common causes: Common causes include Faulty Engine Control Module (ECM), Engine Control Module harness is open or shorted, Engine Control Module circuit poor electrical connection.
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 179

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 24, 2023

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U18C8 2015 GMC Sierra Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device. The Diagnostic Trouble Code (DTC) will be set when a supervised periodic message that includes the transmitter device availability has not been received.

OBDII Code U18C8 2015 GMC Sierra - Glow Plug Control Module Lost Communication with Engine Control Module - AutoCodes.com — U18C8 2015 GMC Sierra Code - Glow Plug Control Module Lost Communication with Engine Control Module

What does this mean?

What are the Possible Causes of the DTC U18C8 2015 GMC Sierra?

Faulty Engine Control Module (ECM)
Engine Control Module harness is open or shorted
Engine Control Module circuit poor electrical connection
Faulty Body Control Module (BCM)

How to Fix the DTC U18C8 2015 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 U18C8 2015 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 U18C8 2015 GMC Sierra code?

Need more information on how to fix the U18C8 2015 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 U18C8 2015 GMC Sierra Code

1. What are the common symptoms of OBDII code U18C8 in a 2015 GMC Sierra?

- Common symptoms include the check engine light illuminating, rough engine performance, difficulty starting the vehicle, and potential loss of power.

2. What does the OBDII code U18C8 indicate in a 2015 GMC Sierra?

- The code U18C8 indicates a communication error between the Glow Plug Control Module (GPCM) and the Engine Control Module (ECM).

3. What are the possible causes of the U18C8 code in a 2015 GMC Sierra?

- Possible causes include damaged wiring or connectors between the GPCM and ECM, a faulty GPCM, a malfunctioning ECM, or software issues.

4. How can I diagnose the U18C8 code in my 2015 GMC Sierra?

- Diagnose the code by conducting a thorough inspection of the wiring and connectors, testing the GPCM and ECM for functionality, and using a diagnostic scanner to retrieve freeze frame data.

5. Can I still drive my 2015 GMC Sierra with the U18C8 code present?

- It is not recommended to drive the vehicle with the U18C8 code present, as it can lead to further damage and potential safety hazards.

6. How can I repair the U18C8 code in my 2015 GMC Sierra?

- Repair options include repairing or replacing damaged wiring, repairing or replacing faulty components such as the GPCM or ECM, and clearing the code with a diagnostic tool.

7. Is it possible to reset the U18C8 code in a 2015 GMC Sierra without fixing the underlying issue?

- While you can clear the code temporarily, it will likely reappear until the underlying communication issue between the GPCM and ECM is resolved.

8. Are there any software updates available to address the U18C8 code in a 2015 GMC Sierra?

- Check with a GMC dealership or authorized service center for any available software updates that may help resolve the communication error between the GPCM and ECM.

9. How much does it typically cost to repair the U18C8 code in a 2015 GMC Sierra?

- The cost of repair can vary depending on the specific issue, but it may range from a few hundred to a few thousand dollars, including parts and labor.

10. Can a DIY enthusiast fix the U18C8 code issue in a 2015 GMC Sierra?

- While some basic troubleshooting steps can be performed by a DIY enthusiast, diagnosing and repairing the U18C8 code may require specialized tools and expertise, so it is recommended to consult a professional mechanic.