C05BB code meaning
Brake Booster Motor A Position Sensor Supply Circuit Range/Performance
Chassis system Generic code C05xx codes Check engine light
What C05BB means
GM uses C05BB in the integrated brake control of 2019 models. There the processor generates two 5 V sensor supplies; each feeds one pedal travel channel plus one motor position channel. C05BB belongs to the second supply (PTS2 and MPS2), C05D1 to the first. GM sets it below 4.85 V or above 5.15 V for 100 ms, and also for an unsteady supply: every out-of-band sample adds 50 points and the fault matures at 800, so after 80 ms at the earliest; every good one subtracts 1, and the fault stays latched until ignition off. All three variants are Type A, MIL on the first trip. GM names a faulty motor position sensor, pedal travel sensor or circuit board as causes. GM thus books its MPS2 under a motor A code, though its MPS2 plausibility fault is C058E.
C05BB at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C05BB
- Check engine lamp and brake warning on the first trip (GM)
- Service brake assist message, hard pedal
- Fault remains until the ignition is switched off
Common causes of C05BB
- Most likelyDefective motor position sensor loading the shared supply
- PossibleDefective pedal travel sensor on the same supply
- PossibleFault on the brake control unit's circuit board
- Less likelyIntermittent contact in the sensor supply wiring
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Booster motor a pos sensor supplyElectric brake boosterBrake pedal position sensor
What each part of C05BB means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| BB | The exact fault in that area. |
What to do next
- Note C05BB 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 C05BB
What does C05BB mean?
C05BB means "Brake Booster Motor A Position Sensor Supply Circuit Range/Performance". GM uses C05BB in the integrated brake control of 2019 models. It is a generic code, so it means the same on every make.
Is it safe to drive with C05BB?
Drive gently and only to a workshop. With C05BB the car can go into limp mode (reduced power) to protect itself.
Will C05BB fail an emissions test?
C05BB 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 C05BB to fix?
Difficulty: workshop only. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will C05BB clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.