C05CD code meaning
Brake Master Cylinder Piston Position Sensor B Circuit Voltage High
Chassis system Generic code C05xx codes Check engine light
What C05CD means
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.
C05CD at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C05CD
- Malfunction indicator lamp and brake warning on GM models
- Booster runs on channel A only or reduces assist
Common causes of C05CD
- Most likelyPWM signal line shorted to supply voltage
- PossibleOutput stage of sensor channel B failed high
- Less likelyMoisture or corrosion bridging pins in the connector
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Master cylinder pos sensor bSensor wiring
What each part of C05CD means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| CD | The exact fault in that area. |
What to do next
- Note C05CD and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C05CD
What does C05CD mean?
C05CD means "Brake Master Cylinder Piston Position Sensor B Circuit Voltage High". Channel B of the master cylinder piston travel sensor is stuck at a permanent high level. It is a generic code, so it means the same on every make.
Is it safe to drive with C05CD?
Drive gently and only to a workshop. With C05CD the car can go into limp mode (reduced power) to protect itself.
Will C05CD fail an emissions test?
C05CD is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C05CD to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will C05CD clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.