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Engine-Codes – Generic – U0129

U0129 Code - Lost Communication with Brake System Control Module

Quick Answer

The U0129 diagnostic trouble code (DTC) indicates that there is a communication error between the vehicle's onboard computer system and the Brake System Control Module. Common causes include Damaged wiring or connectors leading to the Brake System Control Module, Faulty Brake System Control Module, Malfunctioning onboard computer system. 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
U0129 indicates Lost Communication with Brake System Control Module.
Common causes
Common causes include Damaged wiring or connectors leading to the Brake System Control Module, Faulty Brake System Control Module, Malfunctioning onboard computer system.
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 10, 2024
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Code U0129 Description

The U0129 diagnostic trouble code (DTC) indicates that there is a communication error between the vehicle's onboard computer system and the Brake System Control Module. This module is responsible for managing the braking system's operation and ensuring proper function. When communication is lost with this module, it can lead to a variety of issues that can affect the vehicle's performance, safety, and overall drivability.

OBDII Code U0129 - Lost Communication with Brake System Control Module
U0129 Code - Lost Communication with Brake System Control Module

Common Causes of U0129

  1. Damaged wiring or connectors leading to the Brake System Control Module
  2. Faulty Brake System Control Module
  3. Malfunctioning onboard computer system
  4. Software glitches or communication errors within the vehicle's network
  5. Water or moisture intrusion affecting electrical connections

Symptoms of U0129

  1. ABS light, traction control light, or brake warning light illuminated on the dashboard
  2. Erratic braking behavior or reduced braking power
  3. Loss of ABS functionality
  4. Other safety systems affected, such as stability control or adaptive cruise control
  5. Vehicle may experience complete brake failure in extreme cases

How to Fix U0129

  1. Perform a thorough diagnostic scan to retrieve the U0129 code and identify the specific communication issue
  2. Inspect wiring and connectors leading to the Brake System Control Module for any damage or corrosion
  3. Test the Brake System Control Module for proper functionality and communication
  4. Check the onboard computer system for any software glitches or communication errors
  5. Repair or replace any damaged wiring, connectors, or faulty components as needed

Cost to Fix U0129

The cost of repairing a U0129 code can vary depending on the specific cause of the communication error and the extent of the repairs needed. In general, the typical repair costs for this issue can range from $200 to $600, including parts and labor. However, it's important to note that diagnosis time and labor rates at auto repair shops can vary based on factors such as location, vehicle make and model, and engine type. Most auto repair shops charge between $80 and $150 per hour for labor, but rates may be higher in metropolitan areas or at dealerships, while independent shops often offer lower rates. For a more accurate estimate, it's recommended to consult with a local mechanic or repair shop.

What does this mean?

Tech Notes for U0129

When there are problems with the way different systems in a vehicle communicate with each other using a technology called Controller Area Network (CAN) communication, Diagnostic Trouble Codes (DTC) are displayed. These codes can be caused by issues with the main bus or branch of the communication network, or with the Electronic Control Units (ECUs) and sensors that make up the different systems. If you see code for both the CAN communication problems and internal or power source problems at the same time, you should focus on fixing the internal or power source problems first.

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Code U0129 Information for Specific Makes

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 U0129 Code

1. What are the common symptoms of OBDII code U0129 (Lost Communication with Brake System Control Module)?

- Common symptoms include the ABS warning light or traction control light illuminating on the dashboard, loss of ABS or traction control functionality, and potential issues with the brake system.

2. What are some possible causes of OBDII code U0129?

- Potential causes include a faulty brake system control module, damaged wiring or connectors in the communication network, a malfunctioning powertrain control module (PCM), or software issues.

3. How can I diagnose the cause of OBDII code U0129?

- Diagnosis typically involves using a professional diagnostic scanner to retrieve the specific trouble codes, checking for other related codes, inspecting the brake system control module and associated wiring, and testing communication between modules.

4. Can I still drive my vehicle with OBDII code U0129 present?

- It is not recommended to drive the vehicle with this code present, as it may affect the functionality of the brake system and other safety features. Prompt diagnosis and repair are advised.

5. How can I repair OBDII code U0129?

- Repair may involve addressing the root cause of the communication issue, such as replacing the brake system control module, repairing damaged wiring, ensuring proper connections, or reprogramming modules as needed.

6. Is it possible to reset OBDII code U0129 without fixing the underlying issue?

- While clearing the code may temporarily turn off the warning lights, the issue will likely reoccur until the root cause is addressed. It is important to diagnose and repair the problem to prevent safety risks.

7. Are there any DIY fixes for OBDII code U0129?

- DIY fixes may be limited for this code due to the need for specialized diagnostic tools and expertise. It is recommended to consult a professional mechanic for proper diagnosis and repair.

8. Can a low battery voltage cause OBDII code U0129?

- Low battery voltage can potentially cause communication issues between modules, leading to code U0129. Ensuring the battery is in good condition and properly charged is important for optimal system performance.

9. Will OBDII code U0129 cause the vehicle to fail an emissions test?

- While this code itself may not directly impact emissions, it can affect the overall performance and safety of the vehicle. It is advisable to address and resolve the code before undergoing an emissions test.

10. How can I prevent OBDII code U0129 from occurring in the future?

- Regular maintenance, proper care of electrical components, and addressing any warning lights promptly can help prevent issues that may lead to code U0129. Regularly checking the vehicle's diagnostic system is also recommended.

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