C05BDBrake Booster Motor B Position Sensor Supply Circuit Low
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- C05BD means the supply of motor B's position sensor reads below its permitted minimum – a ground short, a sensor pulling excess current or a weak regulator. No manufacturer publishes this code. Hitachi Astemo explains why two supplies need cross-checking: both share one ground, so without comparison the controller could not say which supply sagged. Each microcontroller there reads a 2.5 V reference from its own supply and a 3.75 V monitor of the other, and a low supply leaves a distinct pattern across those four values. A tracking regulator like the TPS7B4253-Q1 from TI holds its output current at a limit during a short, so the voltage drops instead of the part burning out. With channel B lost, the actuator relies on motor A or its first sensor and may lower assist gradually.
- What you may notice
- Brake warning lamp on
- Assist fades gradually or is limited at high demand
- Likely causes
- LikelyMotor B sensor supply line shorted to ground
- PossibleDamaged motor B position sensor drawing too much current
- RareSecond sensor regulator in the control unit weak
- 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.