Chassis, generic

C057A Brake Booster Temperature Sensor B Circuit High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C057A is the high counterpart: temperature channel B of the booster reads at its upper end, which GM interprets as the signal shorted to supply. GM's 2023 and 2025 EBCM tables set it above 3.14 V when five checks in a row fail within 0.6 s and rate it Type B, with MIL after two trips; the 2019 Cadillac XT4 version uses 3.34 V and is Type C without MIL. Channel A trips at 3.27 V under P25C7, so the two channels have slightly different limits. Whether a high voltage means hot or cold depends on where the thermistor sits in its divider, which is why the module treats a value at the rail as a wiring fault rather than a temperature. Without a usable reading the booster cannot protect its motor and may reduce assist.

Likely causes

Temperature signal B shorted to the sensor supply or another voltage
Thermistor or its return line open, pulling the input to the rail
Moisture or corrosion inside the booster electronics

Symptoms

  • Check engine light after two trips (GM 2023/2025) and brake warning
  • Temperature B reading stuck at a limit
  • Reduced brake assist during long downhill braking

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

C0579C057BC057CC057DP25C7

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, passive-components.eu.