C05B8Brake Booster Motor A Position Sensor Supply Circuit/Open
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- The rotor position sensor of booster motor A – Hall, magnetoresistive or a digital SENT angle sensor – is fed from a regulated 5 V output of the brake control unit. C05B8 reports that this feed is interrupted. No manufacturer documents the code publicly; GM's 2019 integrated brake control lists supply faults of its two motor position sensors under C05D1 and C05BB only. Denso's sensor patent shows why an open feed is hard to tell from a dead sensor: with a pull-down input the signal simply falls to 0 V. Hitachi Astemo's steering patent therefore monitors each sensor supply separately so the failed one can be identified. Without a rotor angle the booster cannot commutate its motor, so assist is cut back or lost and the brake warning appears.
- What you may notice
- Brake warning lamp and message such as service brake assist
- Noticeably harder brake pedal
- Regenerative or electronic brake functions unavailable
- Likely causes
- LikelyBroken supply wire or pin between control unit and motor position sensor
- PossibleSensor supply output in the brake control unit failed
- RareInternal open in the position sensor's supply path
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.