Chassis, generic

C058C Brake Booster Motor B Position Sensor Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C058C applies when the motor B position signal sits below its lower limit – usually a sensor line shorted to ground, a missing sensor supply or a damaged sensor element. No manufacturer publishes this code; GM limits its documented position checks to motor A, where C0588 trips in the XT4 module below 1,300 counts. The physics are the same on either side: Hitachi's resolver patent attributes a reading near 0 V to a ground short, and a vector-length check like the one Infineon specifies for its TLE5009 sine/cosine sensor exposes an amplitude that has collapsed. In a dual-winding booster as described by Hyundai Mobis, the inverter for winding B depends on this angle, so the module shuts that inverter down and relies on the remaining channel.

Likely causes

Signal line of sensor B shorted to ground
Supply of sensor B missing or too low
Sensor element B or its magnet degraded, signal amplitude too small

Symptoms

  • Brake warning lamp
  • Assist may continue on one channel with reduced dynamics

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 b pos sensorsensor wiring

Related codes

C058BC058DC058EC0588

References: patents.google.com, infineon.com, patents.google.com.