C05D5Brake Master Cylinder Cut Off Valve
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- Electrical fault of the solenoid valve that separates the master cylinder from the wheel circuits in by-wire operation, so pressure comes from the motor and the pedal works against a simulator. In GM's booster-type EBCMs (XT4, 23OBDG07, 25OBDG03B) the valve driver reports over-current of about 4 to 6.5 A, an output stage above 195-220 °C, a lost power ground or lost freewheeling within 0.03 s. GM's integrated controller maps open and shorted driver tests of its simulator-side valve to C05D5 (Type A, MIL) but a coil above 265 °C as Type C without MIL; 25OBDG04A uses it for the traction control isolation valves. Bosch describes these isolation valves closing during by-wire braking. Expect reduced assist or a mechanical push-through fallback.
- What you may notice
- Malfunction indicator lamp and brake warning
- Loss of brake assist, pedal works on the master cylinder directly
- ESC and traction control limited
- Likely causes
- LikelyValve coil shorted or open inside the hydraulic unit
- PossibleValve driver stage or ASIC in the module defective
- PossiblePoor power ground of the brake module
- RareValve overheated by excessive activation time
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €300 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.