Chassis, generic

C057E Brake Booster Temperature Sensor A/B Correlation

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

With two temperature sensors in the booster the module can cross-check them: after a long rest both should be close to ambient, and under load they should move in a consistent pattern. C057E is set when sensors A and B disagree beyond a plausible margin. GM fits two such channels in its booster (A: P25C6/P25C7, B: C0579/C057A), but its public tables do not list C057E, and no other maker documents it either. The idea is known from related systems: Safran compares redundant temperature sensors in electric brake actuators and discards inconsistent ones, and Hitachi Astemo's electric booster carries separate motor and drive circuit sensors. As the module cannot tell which reading is wrong, it usually protects the motor by reducing assist.

Likely causes

One of the two thermistors drifted or lost thermal contact
Added resistance in one sensor circuit, e.g. corroded contact
Real local overheating of motor or power stage, e.g. after jammed mechanics

Symptoms

  • Brake system warning with service message
  • Temperatures A and B clearly apart on the scan tool after a cold start
  • Reduced brake assist

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,500
Time0.5–4 h

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

Parts involved

brake booster temp sensor belectric brake booster

Related codes

C057CP25C5C0579C057AC05B6

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