What it means
A control module received invalid data from brake system control module B. The code identifies a data validity fault; the specific affected function depends on the vehicle.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Brake system control module B sends information that other modules use for vehicle braking and related control functions. U04B5 is set when a receiving module judges data from module B invalid; the code specifically identifies module B's data path, not every brake control module.
Common causes
Most likely first.
- Fault in the transmitting module
- Network wiring or connector fault
- Module power or ground fault
- Software or configuration mismatch
Symptoms
- A brake-system warning may appear
- One or more brake control functions may be affected
How to diagnose it
- Record freeze-frame data and scan all brake and stability modules for codes that also identify module B or its network.
- Review live data from brake system control module B and note any values shown as invalid or inconsistent with the vehicle state.
- Inspect module B's connectors and network wiring for loose pins, corrosion, water intrusion, or damage.
- Check module B's power and ground against the manufacturer's specification.
- Test the network wiring and connector terminals serving module B for opens, shorts, or poor connections using the wiring information.
- If its wiring and supplies pass, check for software or configuration issues before considering module replacement.
Common fixes
- Reconnect or repair a loose or corroded brake system control module B connector.
- Repair damaged network wiring or connector terminals serving module B.
- Repair a faulty power or ground connection at module B.
- Apply an applicable software or configuration correction.
- Replace brake system control module B only if testing confirms it is the source of invalid data.
Can I keep driving?
Avoid driving if a brake or stability warning appears or braking behavior changes, and arrange recovery if you are unsure the brakes work normally. Invalid data from brake system control module B may disable or limit brake control functions.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.