Chassis, generic

C05BA Brake Booster Motor A Position Sensor Supply Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C05BA covers the opposite case: the 5 V feed of motor A's position sensor rises above its upper limit. The usual culprit is a supply line touching a battery-voltage wire, less often a regulator that has lost control. No manufacturer publishes C05BA; GM's 2019 brake module treats its sensor supplies as high above 5.15 V for 100 ms, filing them under C05D1 or C05BB. TI's TPS7B4253-Q1 tracker shows how such outputs are protected: it survives a short to battery and opens its internal switch within about 1 ms. Hitachi Astemo deliberately places its supply monitor voltage at 3.75 V, below 5 V, so overvoltage stays measurable. An overvoltage can also damage the sensor, so assist is withdrawn and the booster runs without motor support.

Likely causes

Supply line shorted to a battery-voltage circuit in the harness
Sensor supply regulator in the control unit no longer regulating
Poor control unit ground shifting the measured supply voltage

Symptoms

  • Brake warning lamp and assist warning message
  • Hard brake pedal, longer stopping effort

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–3,000
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 booster

Related codes

C05B8C05B9C05BBC05BEC05D1

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