U0129: Lost Communication With Brake System Control Module A
What Does U0129 Mean?
U0129 is a diagnostic trouble code indicating: Lost Communication With Brake System Control Module A. This code relates to the network communication system. It has been reported in NHTSA complaints across 4 different vehicle models.
Common Causes
- 🔍 Sensor or control module malfunction
U0129 Reports by Year
Real Owner Reports
From NHTSA complaint database — actual owner descriptions.
"DRIVER FIRST NOTICED A PROBLEM WHEN SHE CAME TO A STOP AT A TRAFFIC LIGHT. THE CAMRY STARTED REVVING THE ENGINE EVEN THOUGH DRIVER WAS DEPRESSING THE BRAKE PEDAL; AT THIS POINT THE TRACTION LIGHT CAME ON. FIVE MINUTES LATER, DRIVER APPROACHED A RED LIGHT GOING APPROXIMATELY 25 MPH. SHE DEPRESSED "
— Toyota Camry owner, 06/18/2010
"ON 1/8/20 WHEN I STARTED MY CAR IN THE MORNING ALL WARNING LIGHTS CAME ON BEFORE LEAVING THE DRIVEWAY, AND STAYED ON ALL THE WAY TO WORK, AND BACK. THEN AGAIN THE FOLLOWING MORNING. I CALLED HONDA ON 1/9/20, THEY ADVISED TO COME IN SOONER THAN LATER. CAR IS AT HONDA NOW 1/10/20, THEY ARE STATING ALL"
— Honda Cr-V owner, 01/08/2020
"When starting the vehicle, the message center displays "Loss Communications Brake System Control Module A." The vehicle losses power steering, speedometer indication, tire pressure monitoring, and stability control. There are numerous codes displayed for Brake System, Power Steering, Parking Brake"
— Bmw X3 owner, 08/23/2025
Source: NHTSA Complaints Database
Most Reported Vehicles for U0129
Based on NHTSA owner complaint data.
| # | Vehicle | Reports |
|---|---|---|
| 1 | TOYOTA CAMRY | |
| 2 | TOYOTA COROLLA | |
| 3 | HONDA CR-V | |
| 4 | BMW X3 |
Frequently Asked Questions
What causes communication codes?
Can a bad battery cause network codes?
What To Do Next
Possible Fixes
- 🔧 Have the code scanned with a professional-grade scanner to read freeze frame data
- 🔧 Test the relevant sensor(s) with a multimeter before replacing
- 🔧 Check battery voltage and ground connections; inspect CAN bus wiring
- 🔧 If DIY repair isn't feasible, get a diagnostic from a trusted mechanic ($50-150)
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1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.