C05BD code meaning
Brake Booster Motor B Position Sensor Supply Circuit Low
What C05BD means
C05BD means the supply of motor B's position sensor reads below its permitted minimum – a ground short, a sensor pulling excess current or a weak regulator. No manufacturer publishes this code. Hitachi Astemo explains why two supplies need cross-checking: both share one ground, so without comparison the controller could not say which supply sagged. Each microcontroller there reads a 2.5 V reference from its own supply and a 3.75 V monitor of the other, and a low supply leaves a distinct pattern across those four values. A tracking regulator like the TPS7B4253-Q1 from TI holds its output current at a limit during a short, so the voltage drops instead of the part burning out. With channel B lost, the actuator relies on motor A or its first sensor and may lower assist gradually.
C05BD at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C05BD
- Brake warning lamp on
- Assist fades gradually or is limited at high demand
Common causes of C05BD
- Most likelyMotor B sensor supply line shorted to ground
- PossibleDamaged motor B position sensor drawing too much current
- Less likelySecond sensor regulator in the control unit weak
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Booster motor b pos sensor supplyElectric brake booster
What each part of C05BD means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| BD | The exact fault in that area. |
What to do next
- Note C05BD 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 C05BD
What does C05BD mean?
C05BD means "Brake Booster Motor B Position Sensor Supply Circuit Low". C05BD means the supply of motor B's position sensor reads below its permitted minimum – a ground short, a sensor pulling excess current or a weak regulator. It is a generic code, so it means the same on every make.
Is it safe to drive with C05BD?
Drive gently and only to a workshop. With C05BD the car can go into limp mode (reduced power) to protect itself.
Will C05BD fail an emissions test?
C05BD 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 C05BD to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will C05BD clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.