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U0129 Toyota 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 Toyota 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 4,997
How popular is this code, among other codes? Low
What is this?
Table of contents Created and updated by William Orellana on Mar 26, 2023
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Code U0129 Toyota 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 Toyota - Lost Communication with Brake System Control Module - AutoCodes.com
U0129 Toyota Code - Lost Communication with Brake System Control Module
What does this mean?

What are the Possible Causes of the DTC U0129 Toyota?

  • 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 Toyota?

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 Toyota 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 Toyota Models

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 Toyota Code

1. What does the OBDII code U0129 mean on a Toyota?

U0129 indicates a loss of communication with the Brake System Control Module (BSCM), which manages the vehicle's braking functions.

2. What are the symptoms of code U0129 in a Toyota?

Common symptoms include a lit ABS or brake warning light, unresponsive ABS or traction control, and possibly reduced braking performance.

3. What causes the U0129 code in a Toyota?

The code can be triggered by faulty wiring, a damaged Brake System Control Module, communication network issues, or a failing ABS actuator.

4. Can I still drive my Toyota with a U0129 code?

While you may be able to drive, the ABS and traction control systems may not function properly, increasing the risk of an accident, especially in poor driving conditions.

5. How do I diagnose the U0129 code on my Toyota?

Start by checking the wiring and connectors for damage or corrosion, inspect the CAN bus network, and ensure the Brake System Control Module is receiving power.

6. What tools are needed to troubleshoot a U0129 code?

You’ll need an OBDII scanner capable of reading CAN bus communication, a multimeter for testing wiring, and possibly a wiring diagram for your Toyota model.

7. How much does it cost to fix a U0129 code on a Toyota?

Repair costs vary depending on the issue but typically range from $100 for simple wiring repairs to over $1,000 if the Brake System Control Module needs replacement.

8. Can a dead battery cause a U0129 code in a Toyota?

Yes, a weak or dead battery can disrupt communication between modules, potentially triggering the U0129 code.

9. How do I reset the U0129 code on my Toyota?

After resolving the issue, use an OBDII scanner to clear the code. If the problem persists, the code may reappear.

10. What happens if I ignore the U0129 code on my Toyota?

Ignoring this code can lead to unsafe driving conditions due to compromised braking and stability control systems, potentially leading to accidents.

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