Chassis, generic

C05B5 Brake Booster Temperature Sensor C Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

C05B5 is reserved for an interrupted circuit of booster temperature sensor C. No manufacturer documents it publicly; Mitsubishi, the one maker naming sensor C codes, reports problems with this channel only as C05B3 or C05B4. Boosters typically carry several NTC thermistors: Hitachi Astemo places one on the motor and one in the controller near the motor drive stage and caps motor current when either runs hot. If a thermistor or its lead breaks, the divider sits at one rail; a supplier overview cautions that such a rail reading alone cannot separate every wiring, reference or converter fault. Microchip adds that a board or module NTC follows case temperature, not the transistor junction. As the sensor is mostly internal, repair normally means a new booster unit.

Likely causes

Cracked thermistor body or broken lead inside the booster
Fractured solder joint on the control board from vibration or heat cycles
Open wire or pin where the sensor is wired externally

Symptoms

  • Brake or brake system warning lamp on
  • Booster may restrict assist as a precaution, depending on design

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

C05B3C05B4C05B6C05B7C057B

References: passive-components.eu, ww1.microchip.com, patents.google.com, mitsubishitechinfo.com.