Lost Communication With Brake System Control Module
The U0129 code means the vehicle's onboard diagnostic system has detected: Lost Communication With Brake System Control Module. This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- hard
- Estimated cost
- $300 - $1500 (parts and labor)
Network codes mean modules are not communicating. You need a scanner that reads all systems to find the problem.
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Common Symptoms
- ABS, traction control, and stability control lights all on
- Brake warning light illuminated
- Brake pedal feels spongy or unresponsive
- Brake assist and emergency braking disabled
- Vehicle may take longer to stop
Probable Causes (Ranked by Likelihood)
- Failed ABS/brake system control module Very High
- Damaged CAN bus wiring to brake module High
- ABS hydraulic unit internal failure Moderate
- Corroded brake module connector Moderate
- Power supply or ground issue at brake module Low
Step-by-Step Diagnostic Procedure
-
Scan for DTCs in all chassis and brake modules
-
Check power supply and ground at the ABS/brake control module
-
Inspect CAN bus wiring and connector at the brake module
-
Measure CAN bus signal with oscilloscope at the brake module connector
-
Check brake fluid level and condition
Frequently Asked Questions
Can I drive with code U0129?
No. This code indicates the main brake system control module has lost communication. ABS, brake assist, and stability control are all disabled. Have the vehicle towed for repair.
What causes U0129?
A failed ABS module or damaged CAN bus wiring are the most common causes. The ABS hydraulic unit and module are often a combined assembly that must be replaced together.
Is U0129 expensive to fix?
ABS module replacement typically costs $300 to $1500 depending on the vehicle. The module often requires programming to the vehicle, adding to the cost.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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