C05CBBrake Master Cylinder Piston Position Sensor A Circuit Voltage Low
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- Mirror image of C05CA: channel A of the master cylinder piston travel sensor reports that its value fell below the permitted range. GM documents it for its booster-type EBCMs, where the linear position sensor encodes travel digitally and flags its own low limit violation: the XT4 module acts after 0.033 s on the SENT fast channel, while the 2023 and 2025 tables wait 0.96 s for the slow-channel status, Type A, one trip, MIL. A low report often follows a sensor that loses its magnet reference or sees a sagging supply. Bosch builds such travel sensors around a Hall element that tracks a magnetic field over up to 45 mm of rod stroke. If the code returns after wiring checks, the sensor is usually part of the booster unit and replaced with it.
- What you may notice
- Malfunction indicator lamp and brake system message
- Brake assist reduced, regeneration possibly off
- Likely causes
- LikelyPosition sensor A reporting out-of-range low
- PossibleSagging sensor supply voltage
- RareMagnet carrier loose or damaged
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.