C05CDBrake Master Cylinder Piston Position Sensor B Circuit Voltage High
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- Channel B of the master cylinder piston travel sensor is stuck at a permanent high level. In GM's booster-type EBCMs the second channel is not sent over SENT like channel A but as a PWM signal around 1 kHz, which is why high and low here mean a line that no longer toggles: the module sets C05CD when it sees a steady high state for 0.2 s, read as a short of the PWM line to supply (19OBDG03D XT4 section, 23OBDG07, 25OBDG03B; Type A, one trip, MIL). Duty cycle or frequency outside 8.5-92 % or 900-1120 Hz falls under a separate communication code. Look for chafed wiring touching a supply wire or a sensor output stage that has failed high. C05CE is the stuck-low partner.
- What you may notice
- Malfunction indicator lamp and brake warning on GM models
- Booster runs on channel A only or reduces assist
- Likely causes
- LikelyPWM signal line shorted to supply voltage
- PossibleOutput stage of sensor channel B failed high
- RareMoisture or corrosion bridging pins in the connector
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.