What it means
Brake Booster Motor B Phase U-V-W Circuit Range/Performance: the signal is implausible or outside the valid range. The electric brake booster generates the braking assist; a motor or sensor fault can reduce or disable power-assisted braking. Safety-relevant.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
The electric brake booster uses Motor B to provide braking assistance, and its U, V, and W phase circuits drive the motor. The control module sets C0586 when the phase signals are implausible or outside their valid operating range, rather than simply too low or too high.
Common causes
Most likely first.
- Motor winding resistance drifted
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Brake or ABS warning light
- Brake assist may be reduced or unavailable
How to diagnose it
- Use a scan tool to record freeze-frame data and compare Motor B phase live data and related codes to identify when the readings became implausible.
- Inspect Motor B's U, V, and W wiring and connectors for loose terminals, corrosion, damage, or intermittent contact.
- Check the motor or sensor mounting for looseness that could allow vibration to distort the phase readings.
- Test the phase circuits and motor winding condition using the manufacturer's procedures and specifications.
- If the circuits, winding, and mounting pass, test the relevant sensor and control module inputs according to vehicle service information.
Common fixes
- Secure a loose motor or sensor mounting that is disrupting the phase readings.
- Clean or repair corroded, loose, or damaged phase connectors.
- Repair damaged U, V, or W wiring.
- Replace the motor or sensor if tests confirm its readings or winding condition are outside the manufacturer's specification.
- Repair or replace the control module only if its inputs fail the specified tests.
Can I keep driving?
Brake assist may be reduced or unavailable, so avoid driving if pedal effort or braking response has changed. Have the vehicle assessed promptly; a worsening fault can leave you with much less assisted braking.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.