AutoCodes – Generic – U0129

U0129 Code - Lost Communication with Brake System Control Module

Quick Answer

The Controller Area Network (CAN) is a standard bus system in vehicles that enables the connection of automotive devices without the need for a host computer. Common causes include Faulty Controller Area Network (CAN) Communication System, Faulty Brake System Control Module, Brake System 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: U0129 indicates Lost Communication with Brake System Control Module.
Common causes: Common causes include Faulty Controller Area Network (CAN) Communication System, Faulty Brake System Control Module, Brake System 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 65,247

How popular is this code, among other codes? Medium

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 Mar 26, 2023

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code U0129 Description

The Controller Area Network (CAN) is a standard bus system in vehicles that enables the connection of automotive devices without the need for a host computer. The exchange of operating information and commands among devices is facilitated by pre-programmed information about the required message exchange on the serial data circuits. Communication is carried out using two dedicated wires, known as CAN high and CAN low, with both lines carrying 2.5V when the CAN bus is in idle mode. During the transmission of data bits, the CAN high line increases to 3.75V while the CAN low drops to 1.25V, creating a 2.5V differential between the lines. Since communication relies on a voltage differential between the two bus lines, the CAN bus is NOT sensitive to inductive spikes, electrical fields, or other noise. The Diagnostic Trouble Code (DTC) sets when a periodic message from the Brake System Control Module has not been received.

OBDII Code U0129 - Lost Communication with Brake System Control Module - AutoCodes.com — U0129 Code - Lost Communication with Brake System Control Module

What does this mean?

What are the Possible Causes of the DTC U0129?

Faulty Controller Area Network (CAN) Communication System
Faulty Brake System Control Module
Brake System Control Module harness is open or shorted
Brake System Control Module circuit poor electrical connection

How to Fix the DTC U0129?

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 does this mean?

Code Tech Notes

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.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the U0129 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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Information for Specific Makes

U0129 Buick — Lost Communication with Brake System Control Module
U0129 Cadillac — Lost Communication with Brake System Control Module
U0129 Chevrolet — Lost Communication with Brake System Control Module
U0129 Ford — Lost Communication With Brake System Control Module
U0129 GMC — Lost Communication with Brake System Control Module
U0129 Lexus — Lost Communication with Brake System Control Module
U0129 Lincoln — Lost Communication With Brake System Control Module
U0129 Mercury — Lost Communication With Brake System Control Module
U0129 Toyota — Lost Communication with Brake System Control Module

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.