C0587Brake Booster Motor A Position Sensor Circuit/Open
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- C0587 concerns the rotor position sensor of booster motor A – a resolver, a sine/cosine magnetic sensor or a set of Hall elements that tells the controller where the rotor stands so it can commutate the windings. The code reports an open sensor circuit. No manufacturer documents it publicly: GM books position faults of this motor under C0588, C0589 and C058A, and C0587 appears in GM's older keyword list only from a different numbering. Hitachi's resolver patent shows how a break is caught: a bias placed on one winding terminal must reappear at the other, otherwise a pull-up drives the reading high. Bosch describes a fallback for a booster whose rotor sensor goes silent – the motor is run open-loop with capped speed and speed changes, so assist becomes weaker.
- What you may notice
- Electric brake assist reduced or off, hard pedal
- Brake warning lamp and message
- Likely causes
- LikelyBroken signal or supply wire of the position sensor
- PossiblePushed-back or corroded pin at the sensor or module connector
- PossibleSensor element inside the booster failed, booster unit usually replaced
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.