Chassis, generic

C0588 Brake Booster Motor A Position Sensor Circuit Low

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0588 is set when the position signal of booster motor A sits below its valid band. GM documents it in its EBCM tables: the 2019 Cadillac XT4 unit trips when a raw sine or cosine value drops under 1,300 counts, or their sum under 3,876, for 10 ms; the 2023 and 2025 tables use a cosine value under 10 counts for 0.15 s, a sine line under 1.047 V or a vector length below 0.25. GM rates every variant Type A, lighting the MIL on the first trip. A low value points to a grounded signal line or missing sensor supply; Hitachi's resolver patent notes that a ground short pulls the output to 0 V. Infineon's TLE5009, a sine/cosine angle sensor intended for motor commutation, specifies a valid vector band for the same reason. Assist is cut or limited, and often the booster unit must be replaced.

Likely causes

Sine or cosine line of the sensor shorted to ground
Missing sensor supply, signals collapse toward zero
Sensor element or target magnet damaged, amplitude too small

Symptoms

  • Check engine lamp together with brake/ABS warning (GM)
  • Electric assist switched off, high pedal effort

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

C0587C0589C058AC058C

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