C057ABrake Booster Temperature Sensor B Circuit High
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyTemperature signal B shorted to the sensor supply or another voltage
- PossibleThermistor or its return line open, pulling the input to the rail
- RareMoisture or corrosion inside the booster electronics
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.