U01B4 — Lost Communication With Brake System Control Module B

What Does U01B4 Mean?

U01B4 is a diagnostic trouble code indicating: Lost Communication With Brake System Control Module B. This code relates to the network communication system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of U01B4

⚠️ Check Engine Light (MIL) illuminated
⚠️ No communication with Brake System Control Module B
⚠️ Multiple warning lights may illuminate simultaneously
⚠️ Related system completely inoperative
⚠️ Multiple warning lights on dashboard

Common Causes

🔍 CAN bus wiring fault (open or shorted) to Brake System Control Module B
🔍 Power or ground supply issue to Brake System Control Module B
🔍 Brake System Control Module B internal failure
🔍 Water intrusion damaging module or connectors
🔍 CAN bus termination resistor fault

Frequently Asked Questions

What does U01B4 mean?

U01B4 indicates: Lost Communication With Brake System Control Module B. The vehicle's computer has detected that the Brake System Control Module B is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code U01B4?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with U01B4 for extended periods may cause additional problems.

How much does it cost to fix U01B4?

Repair costs for U01B4 typically range from $80 to $1200, depending on the root cause. Simple wiring or connector repairs are on the lower end, while component replacement costs more. A proper diagnosis ($80–$150 at most shops) will identify the exact cause before committing to expensive parts.

What To Do Next

Possible Fixes

🔧 Inspect CAN bus wiring to Brake System Control Module B for damage
🔧 Check power and ground supply to Brake System Control Module B
🔧 Replace failed Brake System Control Module B

1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

U01B4: Lost Communication With Brake System Control Module B