AutoCodes – GMC – U1128 GMC

U1128 GMC Code - Lost Communications With Radio

Quick Answer

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Common causes include Faulty Radio, Radio harness is open or shorted, Radio 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: U1128 GMC indicates Lost Communications With Radio.
Common causes: Common causes include Faulty Radio, Radio harness is open or shorted, Radio 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 1,047

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 Apr 22, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U1128 GMC Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for the state of health monitoring/node alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that module node alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a Diagnostic Trouble Code (DTC) U1128 is set.

OBDII Code U1128 GMC - Lost Communications With Radio - AutoCodes.com — U1128 GMC Code - Lost Communications With Radio

What does this mean?

What are the Possible Causes of the DTC U1128 GMC?

Faulty Radio
Radio harness is open or shorted
Radio circuit poor electrical connection

How to Fix the DTC U1128 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 U1128 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.

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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 U1128 GMC Code

1. What are the common symptoms of OBDII code U1128 GMC (Lost Communications With Radio)?

- Common symptoms include radio not working, loss of communication with other modules, and warning lights on the dashboard.

2. What are some possible causes of the U1128 GMC trouble code?

- Possible causes may include a faulty radio unit, damaged wiring or connectors, a bad fuse, or a malfunctioning communication module.

3. How can I diagnose the U1128 GMC code related to lost communications with the radio?

- You can start by checking the radio connections, fuses, and wiring harness for any visible damage. Using a diagnostic scanner to check for communication errors between modules is also recommended.

4. Can a dead battery cause the U1128 GMC trouble code to appear?

- Yes, a dead or low battery can sometimes trigger communication issues between modules, leading to the U1128 code being stored in the system.

5. Is it safe to continue driving with the U1128 GMC code present?

- While the vehicle may still be operable with this code, it is recommended to address the issue promptly as it may affect the overall functionality of the vehicle's electronic systems.

6. What are some repair tips for addressing the U1128 GMC code?

- Start by checking and repairing any damaged wiring or connectors related to the radio system. Resetting the code using a diagnostic scanner after making repairs can help clear the issue.

7. Can I reset the U1128 GMC trouble code myself?

- Yes, you can use an OBDII scanner to reset the code after addressing the underlying issue with the radio communication. However, if the problem persists, further diagnosis may be required.

8. Will disconnecting the battery reset the U1128 GMC trouble code?

- Disconnecting the battery may reset the code temporarily, but it is important to address the root cause of the communication issue to prevent the code from reappearing.

9. How much does it typically cost to repair the U1128 GMC trouble code?

- The cost of repair can vary depending on the underlying cause of the communication issue. Simple fixes like repairing wiring may be relatively inexpensive, while replacing the radio unit could be more costly.

10. Can a DIY enthusiast fix the U1128 GMC trouble code issue?

- Depending on the specific cause of the code, DIY enthusiasts with automotive repair knowledge may be able to address the U1128 GMC issue by checking connections, fuses, and wiring before seeking professional help if needed.