C05BFBrake Booster Motor B Position Sensor Supply Circuit Range/Performance
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- C05BF concerns a motor B sensor supply that stays inside its hard limits but behaves implausibly – it fluctuates, disagrees with the independent monitor, or does not match the first supply. No manufacturer documents C05BF publicly. GM's comparable check for its own two supplies, filed under C05BB and C05D1, shows the principle: brief excursions outside 4.85–5.15 V are weighted and accumulated, while good samples slowly reverse the count, so only a persistent disturbance latches. Hitachi Astemo chooses non-overlapping A/D windows of 475–575 and 699–849 counts for reference and monitor signals so that even a stuck comparator input is caught. A supply that drifts or ripples can corrupt the rotor angle without tripping simple low or high checks, so the module treats channel B as unreliable.
- What you may notice
- Brake warning lamp appearing at times
- Assist occasionally reduced, code returns after clearing
- Likely causes
- LikelyIntermittent contact or corrosion in the motor B sensor supply wiring
- PossibleUnstable sensor supply regulator or failing filter capacitor in the control unit
- RareFault in the supply monitoring circuit itself
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.