Chassis, generic

C05B6 Brake Booster Temperature Sensor C Circuit Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Thermistor resistance drifted through ageing, moisture or micro-cracks
Sensor lost thermal contact with the part it should measure
Thermal model or calibration in the booster control unit not matching the hardware

Symptoms

  • Brake system warning lamp on
  • Assist reduced earlier than usual during long descents or repeated braking

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–2,500
Time1–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

brake booster temp sensor celectric brake booster

Related codes

C05B3C05B4C05B5C05B7C057C

References: patents.google.com, ww1.microchip.com, analogtechnologies.com.