C05B8: Brake Booster Motor A Position Sensor Supply Circuit/Open
Brake Booster Motor A Position Sensor Supply Circuit/Open: the circuit is open. The electric brake booster generates the braking assist; a motor or sensor fault can reduce or disable power-assisted braking. Safety-relevant.
What C05B8 means
C05B8 is a generic OBD-II chassis code in the ABS & brakes group. In plain English: the computer found an electrical fault in that circuit: an open, short or bad connection, or a failed component.
- Check engine light
- Usually on
- Emissions-related
- No
- Limp mode possible
- Yes
- Drive cycle to clear
- Not required
Get it fixed
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Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Common causes
- 01Supply wire openMost likely
- 02Pin pushed back out of connector bodyLess likely
- 03Cracked solder joint inside the module or sensorLess likely
Can I drive with C05B8?
Drive carefully and get it checked soon.
Normal hydraulic braking usually still works, but ABS, stability control or brake assist may be off. Leave extra stopping distance, especially on wet or icy roads. If the pedal feels soft or the red brake light is on, stop driving.
Why we rate it urgent
- ABS or brake assist may be disabled
- Can put the vehicle in limp mode (reduced power)
- Turns on the check engine light
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose C05B8
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just C05B8. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for C05BC. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Test the circuit
Inspect the wiring and connector at the booster motor a pos sensor supply for damage, corrosion or chafing. With a multimeter, check supply voltage, ground and signal against the specifications in the service manual for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Supply wire open; pin pushed back out of connector body; cracked solder joint inside the module or sensor. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
C05B8 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Hard
- Good DIY job?
- Usually a shop job
Involved testing or major parts. Most owners use a shop.
Parts and systems involved
- Booster motor A pos sensor supply
C05B8 FAQ
What does C05B8 mean?
C05B8 means “Brake Booster Motor A Position Sensor Supply Circuit/Open”. Brake Booster Motor A Position Sensor Supply Circuit/Open: the circuit is open. The electric brake booster generates the braking assist; a motor or sensor fault can reduce or disable power-assisted braking. Safety-relevant.
Is C05B8 serious? Can I keep driving?
We rate C05B8 as urgent severity. Drive carefully and get it checked soon. Normal hydraulic braking usually still works, but ABS, stability control or brake assist may be off. Leave extra stopping distance, especially on wet or icy roads. If the pedal feels soft or the red brake light is on, stop driving.
What causes C05B8?
The most common causes, from most to least likely: Supply wire open; Pin pushed back out of connector body; Cracked solder joint inside the module or sensor. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix C05B8?
Typical labor is about $125–$625 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix C05B8 myself?
DIY difficulty is hard. Most owners leave this to a shop because it needs involved testing or specialist tools. Always confirm the cause before buying parts.
Will C05B8 clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.