C057FBrake Booster Motor A Phase U-V-W Circuit/Open
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- C057F covers an interrupted drive path in the three-phase motor of an electric brake booster: a winding, a phase lead or a power transistor that no longer carries current. GM documents it in several brake modules, always as Type A with MIL after one trip. Its 2016 and 2019 hybrid tables switch single bridge transistors while the motor is not being driven and set the code within 5 ms if the phase W voltage does not respond. The 2023 and 2025 EBCM tables measure coil resistance and trip above 0.20358 Ω (or below 0.01258 Ω) for 0.12 s, or when the voltage vector is off by more than 1.5 V. In GM's 2019 IBC unit C057F also covers phases that fail to rise above 3.46 V or sit near battery level before start-up. The brakes keep working, only without electric assist.
- What you may notice
- Hard brake pedal, noticeably more pedal force needed
- Brake system, ABS/traction and check engine lamps on
- Message about reduced brake assist
- Likely causes
- LikelyBridge transistor in the brake module no longer switching (drive stage defect)
- PossibleBroken winding or failed internal phase connection in booster motor A
- PossibleCorroded or loose phase contact between control unit and motor, raising coil resistance
- Repair
- Hard · Usually a job for a workshop.Typical cost: €200 – €2,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.