C05B6 code meaning
Brake Booster Temperature Sensor C Circuit Range/Performance
What C05B6 means
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.
C05B6 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of C05B6
- Brake system warning lamp on
- Assist reduced earlier than usual during long descents or repeated braking
Common causes of C05B6
- Most likelyThermistor resistance drifted through ageing, moisture or micro-cracks
- PossibleSensor lost thermal contact with the part it should measure
- Less likelyThermal model or calibration in the booster control unit not matching the hardware
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake booster temp sensor cElectric brake booster
What each part of C05B6 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B6 | The exact fault in that area. |
What to do next
- Note C05B6 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 C05B6
What does C05B6 mean?
C05B6 means "Brake Booster Temperature Sensor C Circuit Range/Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with C05B6?
Drive gently and only to a workshop. With C05B6 the car can go into limp mode (reduced power) to protect itself.
Will C05B6 fail an emissions test?
C05B6 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 C05B6 to fix?
Difficulty: hard. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will C05B6 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.