Chassis, generic

C0587 Brake Booster Motor A Position Sensor Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Broken signal or supply wire of the position sensor
Pushed-back or corroded pin at the sensor or module connector
Sensor element inside the booster failed, booster unit usually replaced

Symptoms

  • Electric brake assist reduced or off, hard pedal
  • Brake warning lamp and message

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,800
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

booster motor a pos sensorsensor wiring

Related codes

C0588C0589C058AC058B

References: patents.google.com, patents.google.com, nxp.com, patents.google.com.