C05B6Brake Booster Temperature Sensor C Circuit Range/Performance
- Generic OBD-II code · Chassis
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- C05B6 targets a sensor C reading that is electrically inside its band yet does not behave like a real temperature: it stays flat during long assist phases, lags far behind the other channels, or contradicts the thermal estimate of the module. No manufacturer publishes this code. The risk is clear from Hitachi Astemo's booster patent, where measured motor and controller temperatures decide when motor current is cut back and when full assist returns; a believable but wrong value either throttles assist early or lets the drive overheat. Microchip notes that an NTC mounted in a power module tracks the case and heatsink, so a junction estimate has to be derived from it. Long-term drift through moisture or cracking is a known NTC weakness. A plausibility fault normally needs a drive with booster activity to set.
- What you may notice
- Brake system warning lamp on
- Assist reduced earlier than usual during long descents or repeated braking
- Likely causes
- LikelyThermistor resistance drifted through ageing, moisture or micro-cracks
- PossibleSensor lost thermal contact with the part it should measure
- RareThermal model or calibration in the booster control unit not matching the hardware
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.