C058E: Brake Booster Motor B Position Sensor Circuit Range/Performance
What to do
Test the pedal gently before you drive, at a standstill, and expect it to feel normal — but be ready for it not to.
Your car uses an electric motor to assist braking rather than engine vacuum. If that assistance drops out, the brakes still work, but the pedal becomes very hard and takes a great deal more effort, and the car takes longer to stop.
Drive as though that could happen at any moment: much more following distance, gentle speeds, and press the pedal harder than instinct suggests if it goes solid. Do not put off getting this looked at, and if the pedal is already hard, have the car recovered rather than driven.
On a hybrid or electric car, also expect regenerative braking to be reduced or gone, which changes how the car slows when you lift off. Mention that if you notice it — it is part of the same fault.
What this code means
Brake booster motor B's position sensor is reporting an implausible value.
An electric brake booster is what replaced vacuum assistance on cars that have no vacuum to offer.
A petrol engine throttles its intake and produces manifold vacuum as a by-product, and traditional brake servos simply used it. A diesel needs a dedicated pump; a hybrid or electric car, whose engine may be off or absent entirely, has nothing — so the assistance comes from an electric motor pushing the master cylinder directly.
Which makes this motor a genuine safety-critical actuator rather than a convenience. It is a brushless motor with phase windings and a position sensor, controlled precisely, because it is standing between the pedal and the brakes.
Every such system has a mechanical fallback, and knowing it matters. With assistance lost the pedal still acts on the hydraulics directly — so the brakes work, but the pedal becomes very hard and needs far more effort, and stopping distances lengthen considerably. That is a designed failure mode, not a failure of design, and it is why these faults are urgent without being an emergency.
The position sensor is how the controller knows where the motor has pushed the master cylinder to, and therefore how much assistance is actually being delivered. Without a trustworthy position, precise assistance is impossible — so the system withdraws it rather than apply an unknown amount of force to the brakes.
The letter matters here more than usual. A system with two position sensors is using them as a cross-check on a safety-critical actuator, so one failing leaves a car that can still verify itself through the other — which is why the response may be a warning rather than a full fallback. Both failing is a different situation.
Why this page exists when its neighbours do not. Nothing in the public web documents this block — four independent searches established that on 2026-08-10. This code is written because a manufacturer named it, with its definition, in a technical service bulletin filed with the US road safety regulator, and that OEM wording agrees with the standard's own enumeration. Its neighbours have no such document, so they remain undocumented rather than guessed.
Likely causes
Start here
- Corroded or loose connector · specialist
Less common
- Damaged wiring harness · moderate
- Failed power or earth supply to the module · specialist
- Faulty brake system control module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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