U01B3: Lost Communication With Brake Blending Actuator

What it means

ECU lost communication with the brake blending actuator (modulates between regen and friction braking on hybrids/EVs).

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

The brake blending actuator coordinates regenerative braking with friction braking on some hybrids and EVs. This code sets when expected messages from the actuator are missing, so the vehicle may not be able to coordinate the two braking sources as intended.

Common causes

Most likely first.

1. Actuator unpowered or wiring broken
2. Gateway module routing CAN messages incorrectly
3. 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

1. Scan all modules and note freeze-frame data and brake-system warnings before moving the vehicle.
2. Check whether the brake blending actuator responds to a scan tool and whether related braking data is available.
3. Inspect the actuator's connector and harness for damage, corrosion, looseness, or water entry.
4. Check the actuator's power and ground circuits against the manufacturer's specification.
5. If supplies are correct, have the communication wiring and gateway path tested; do not disconnect or probe high-voltage components.

Common fixes

• Secure or repair a loose, corroded actuator connector.
• Repair damaged actuator wiring or its power and ground supply.
• Repair a confirmed communication network or gateway fault.
• Replace the actuator if it fails communication checks with verified circuits.

Can I keep driving?

Treat this as a braking-system fault: braking feel or regenerative braking may change, and stopping behavior may be affected. Avoid driving and arrange safe recovery if a brake warning is present, the pedal feels abnormal, or braking performance changes.