Chassis, generic

C05BB Brake Booster Motor A Position Sensor Supply Circuit Range/Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

GM uses C05BB in the integrated brake control of 2019 models. There the processor generates two 5 V sensor supplies; each feeds one pedal travel channel plus one motor position channel. C05BB belongs to the second supply (PTS2 and MPS2), C05D1 to the first. GM sets it below 4.85 V or above 5.15 V for 100 ms, and also for an unsteady supply: every out-of-band sample adds 50 points and the fault matures at 800, so after 80 ms at the earliest; every good one subtracts 1, and the fault stays latched until ignition off. All three variants are Type A, MIL on the first trip. GM names a faulty motor position sensor, pedal travel sensor or circuit board as causes. GM thus books its MPS2 under a motor A code, though its MPS2 plausibility fault is C058E.

Likely causes

Defective motor position sensor loading the shared supply
Defective pedal travel sensor on the same supply
Fault on the brake control unit's circuit board
Intermittent contact in the sensor supply wiring

Symptoms

  • Check engine lamp and brake warning on the first trip (GM)
  • Service brake assist message, hard pedal
  • Fault remains until the ignition is switched off

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€200–3,000
Time1–4 h

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

Parts involved

booster motor a pos sensor supplyelectric brake boosterbrake pedal position sensor

Related codes

C05B8C05B9C05BAC05BFC05D1C058E

References: gsi.ext.gm.com, patents.google.com, ti.com.