U01B3 code meaning
Lost Communication With Brake Blending Actuator
Network system Generic code U01xx codes Check engine light
What U01B3 means
The brake blending actuator divides each braking request between regeneration by the drive motor and the friction brakes, keeping pedal feel steady while the share shifts. Bosch states that its electromechanical iBooster, together with the ESP hev unit, can blend up to 0.3 g of deceleration. U01B3 is stored when the unit coordinating the brakes, normally the hybrid or brake controller, no longer hears this actuator. No manufacturer documents the code publicly. Lost recuperation raises energy use and, on hybrids, engine running time, and CARB 1968.2 expects hybrid systems to detect faults that disable regenerative braking. The friction brakes then do all the work: expect weaker recuperation, a changed pedal and a brake or hybrid warning. U04B4 is the invalid-data code.
U01B3 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U01B3
- Little or no regenerative braking
- Changed brake pedal feel
- Brake or hybrid system warning
Common causes of U01B3
- Most likelyCAN wiring or connector fault at the brake actuator
- PossibleActuator without supply voltage, often after low 12 V voltage
- Less likelyBrake blending actuator electronics faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake blending actuatorCAN bus
What each part of U01B3 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B3 | The exact fault in that area. |
What to do next
- Note U01B3 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U01B3
What does U01B3 mean?
U01B3 means "Lost Communication With Brake Blending Actuator". The brake blending actuator divides each braking request between regeneration by the drive motor and the friction brakes, keeping pedal feel steady while the share shifts. It is a generic code, so it means the same on every make.
Is it safe to drive with U01B3?
Drive gently and only to a workshop. With U01B3 the car can go into limp mode (reduced power) to protect itself.
Will U01B3 fail an emissions test?
Yes, it can. U01B3 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U01B3 to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will U01B3 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.