What it means
ECU lost communication with brake system control module B (secondary brake controller). A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.
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 is a secondary brake controller that exchanges information with other vehicle modules. This code sets when expected messages from module B are missing, which can disable functions that depend on its brake data.
Common causes
Most likely first.
- Module unpowered
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and capture freeze-frame data, checking for other brake-controller or network faults.
- Check whether Brake System Control Module B responds to a scan tool and whether its brake data is available.
- Inspect module B's connector and harness for damage, corrosion, looseness, or water entry.
- Check the module's power and ground circuits under load against the manufacturer's specification.
- If supplies are sound, test the relevant network wiring and gateway routing; avoid driving if brake warnings or abnormal braking are present.
Common fixes
- Reconnect or repair module B's loose or corroded connector.
- Repair damaged wiring or restore module B's power and ground.
- Repair a confirmed network or gateway routing fault.
- Replace Brake System Control Module B if it remains offline with verified circuits.
Can I keep driving?
Because module B is part of brake control, a communication loss can affect dependent braking functions or trigger reduced operation. Do not drive if the brake warning is on, the pedal feels different, or stopping performance is reduced; arrange recovery and diagnosis.
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.