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Engine-Codes – GMC – U1556 GMC

U1556 GMC Code - Chassis Control Module Lost Communication With Trailer Brake Power Control Module On LIN Bus

Quick Answer

The U1556 GMC code indicates that the Chassis Control Module (CCM) has lost communication with the Trailer Brake Power Control Module on the Local Interconnect Network (LIN) bus. Common causes include Faulty wiring or connections in the LIN bus network, Defective Chassis Control Module, Trailer Brake Power Control Module failure. 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
U1556 GMC indicates Chassis Control Module Lost Communication With Trailer Brake Power Control Module On LIN Bus.
Common causes
Common causes include Faulty wiring or connections in the LIN bus network, Defective Chassis Control Module, Trailer Brake Power Control Module failure.
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.
What is this?
Table of contents Created and updated by William Orellana on Sep 13, 2024
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Code U1556 GMC Description

The U1556 GMC code indicates that the Chassis Control Module (CCM) has lost communication with the Trailer Brake Power Control Module on the Local Interconnect Network (LIN) bus. The LIN bus is a communication network used in modern vehicles to allow various control modules to communicate with each other. In this case, the CCM, which is responsible for controlling various chassis-related functions, is unable to communicate with the Trailer Brake Power Control Module, which manages the trailer brake system.

OBDII Code U1556 GMC - Chassis Control Module Lost Communication With Trailer Brake Power Control Module On LIN Bus
U1556 GMC Code - Chassis Control Module Lost Communication With Trailer Brake Power Control Module On LIN Bus

Common Causes of U1556 GMC

  1. Faulty wiring or connections in the LIN bus network
  2. Defective Chassis Control Module
  3. Trailer Brake Power Control Module failure
  4. Software issues in the control modules
  5. Corrosion or damage to the control module connectors

Symptoms of U1556 GMC

  1. Trailer brake system malfunction
  2. ABS warning light illuminated on the dashboard
  3. Loss of stability control or traction control functions
  4. Inability to tow a trailer safely
  5. Erratic behavior of chassis-related systems

How to Fix U1556 GMC

  1. Diagnose the specific cause of the communication loss using a diagnostic scanner capable of reading manufacturer-specific codes.
  2. Inspect the wiring and connections in the LIN bus network for any damage or corrosion, repairing or replacing as necessary.
  3. Test the Chassis Control Module and Trailer Brake Power Control Module for proper functionality, replacing any faulty modules.
  4. Update the software in the control modules to the latest version, if applicable.
  5. Clear the code from the vehicle's memory and perform a test drive to ensure proper communication between the modules.

Cost to Fix U1556 GMC

The typical repair costs for addressing the U1556 GMC code can vary depending on the specific cause of the communication loss. In general, the cost of parts such as control modules or wiring harnesses can range from $200 to $800, while labor costs can add an additional $100 to $300. Overall, the total repair cost for this issue may fall within the range of $300 to $1100. It is important to note that these are rough estimates, and actual costs may vary based on factors such as location, vehicle make and model, and the extent of the repairs needed. It is recommended to consult with a qualified mechanic or auto repair shop for a more accurate cost estimate based on the specific circumstances of the vehicle in question.

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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 U1556 GMC Code

1. What are the common symptoms of OBDII code U1556 GMC?

The common symptoms of code U1556 include issues with the trailer brake system, loss of communication with the chassis control module, and warning lights on the dashboard.

2. What can cause the Chassis Control Module to lose communication with the Trailer Brake Power Control Module on the LIN bus?

The loss of communication between the Chassis Control Module and Trailer Brake Power Control Module can be caused by damaged wiring, a faulty control module, or a communication network issue.

3. How can I diagnose the U1556 GMC code?

Diagnosing code U1556 typically involves checking the wiring connections between the chassis control module and trailer brake power control module, testing the control modules for functionality, and verifying the LIN bus communication network.

4. What is the LIN bus in relation to OBDII code U1556?

The LIN bus is a communication network used by various control modules in a vehicle to exchange data. In the case of code U1556, it refers to the communication link between the chassis control module and the trailer brake power control module.

5. Can I still drive my vehicle with code U1556 present?

It is not recommended to drive your vehicle with code U1556 present, as it can affect the functionality of critical systems like the trailer brake system. It is best to address the issue promptly to ensure safe operation.

6. How can I repair OBDII code U1556 GMC?

Repairing code U1556 involves identifying and fixing the root cause of the communication loss, which may include repairing or replacing damaged wiring, addressing control module issues, or resolving communication network problems.

7. Is it necessary to visit a mechanic for code U1556 GMC?

While some DIY enthusiasts may be able to diagnose and repair code U1556 themselves, it is generally recommended to seek the expertise of a qualified mechanic or technician to ensure proper diagnosis and repair of the issue.

8. Will resetting the OBDII code U1556 clear the problem?

Simply resetting the OBDII code U1556 may temporarily clear the warning lights, but it will not fix the underlying issue causing the communication loss between the chassis control module and trailer brake power control module.

9. Can extreme weather conditions cause code U1556 to trigger?

Extreme weather conditions, such as excessive heat or moisture, can potentially affect the electrical connections and components involved in the LIN bus communication network, leading to code U1556 being triggered.

10. How can I prevent OBDII code U1556 from occurring in the future?

To prevent code U1556 from occurring in the future, it is essential to perform regular vehicle inspections, address any wiring issues promptly, and ensure proper maintenance of the control modules and communication network.

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