Chassis, generic

C0589 Brake Booster Motor A Position Sensor Circuit High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0589 is the high counterpart: a sine or cosine line of motor A's position sensor reads above its permitted maximum. In GM's 2019 XT4 brake module a raw value above 2,795 counts, or a sum above 4,327, for 10 ms sets it; the 2023 and 2025 EBCM tables trip on a cosine reading above 4,075 counts lasting 0.15 s, a sine input above 2.252 V, or a calculated vector length above 1.14. GM classifies it as Type A, MIL on the first trip. Typical causes are a sensor line touching supply voltage or a broken sensor ground. Hitachi describes how a short to battery drives the evaluated signal to its upper limit, after which motor current is cut. Without a trustworthy rotor angle the booster cannot commutate its motor, so electric assist is withdrawn.

Likely causes

Sensor signal line shorted to the sensor supply or battery voltage
Open sensor ground lifting the signals to the upper limit
Internal sensor fault in the booster unit

Symptoms

  • Brake assist warning with check engine lamp (GM)
  • Hard pedal, assist withdrawn

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

C0587C0588C058AC058D

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