What it means
Brake Booster Motor B Phase U-V-W Current Low: the control module has detected this fault condition. 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
Brake booster motor B provides power-assist force, with U, V, and W phase circuits carrying the current that runs the motor. The control module monitors phase current; C0593 sets when motor B current is lower than expected, which can indicate an open or high-resistance connection in one of its phase paths.
Common causes
Most likely first.
- Open or high resistance in motor B phase wiring
- Poor motor connector contact
- Motor winding fault
- Control module fault
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Capture freeze-frame data and related booster codes to confirm whether low motor B current occurred while the module commanded the motor to run.
- Inspect motor B phase connectors and wiring for loose contacts, corrosion, broken conductors, or visible damage.
- Check terminal fit and contact condition at the motor B connector because poor contact can limit phase current.
- Measure continuity and resistance through each motor B U, V, and W phase path and compare with the manufacturer's specifications.
- If the phase wiring is sound, test motor B windings and the drive circuit under the manufacturer's procedure before assessing the control module.
Common fixes
- Secure or restore a loose or corroded motor B phase connector contact.
- Repair an open or high-resistance motor B phase wire.
- Replace motor B if its winding checks fail the manufacturer's specifications.
- Repair or replace the motor drive circuit or control module only after the motor and phase wiring pass testing.
Can I keep driving?
Low current can leave motor B unable to provide the expected brake assist, increasing pedal effort or reducing assistance. Avoid driving if assist is reduced or the brake warning is lit, and arrange prompt diagnosis.
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.