Damaged or corroded wiring in the brake booster motor phase harness, particularly at connectors or where the loom flexes; A failing brake booster motor with worn brushes, shorted windings, or internal phase-to-phase faults; Poor ground connection for the booster motor or its control module, causing voltage drops under load; A faulty brake booster control module that misreads phase current or fails to output a clean drive signal; Water intrusion or debris in the motor connector causing intermittent phase shorts; A weak or failing 12-volt battery or charging system that drops voltage during high-current motor operation

DTC codes / C05xx · Brakes, steering and suspension / C0586

C0586Brake Booster Motor B Phase U-V-W Circuit Range/Performance

Q: What does code C0586 mean?

Brake Booster Motor B Phase U-V-W Circuit Range/Performance. C0586 indicates that the brake booster motor's three-phase (U, V, W) electrical circuit has a range or performance fault, meaning the control module detected an abnormal voltage, current, or phase relationship while commanding the motor. The computer expects balanced phase currents and a predictable response during self-tests or brake assist events, and this code sets when those values fall outside the allowed window.

C0586 indicates that the brake booster motor's three-phase (U, V, W) electrical circuit has a range or performance fault, meaning the control module detected an abnormal voltage, current, or phase relationship while commanding the motor. The computer expects balanced phase currents and a predictable response during self-tests or brake assist events, and this code sets when those values fall outside the allowed window.

SystemChassis

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaBrakes, steering and suspension

Symptoms you may notice

Illumination of the brake system warning light, often accompanied by a chime
Reduced or absent brake assist, requiring noticeably higher pedal effort
A hard brake pedal that feels unresponsive during the first press
Intermittent assist loss that may clear after the vehicle is restarted
Often no symptoms besides the warning light, especially if the fault is stored but not currently active

Common causes, most likely first

Damaged or corroded wiring in the brake booster motor phase harness, particularly at connectors or where the loom flexes
A failing brake booster motor with worn brushes, shorted windings, or internal phase-to-phase faults
Poor ground connection for the booster motor or its control module, causing voltage drops under load
A faulty brake booster control module that misreads phase current or fails to output a clean drive signal
Water intrusion or debris in the motor connector causing intermittent phase shorts
A weak or failing 12-volt battery or charging system that drops voltage during high-current motor operation

How to diagnose and fix it

Perform a thorough visual inspection of the booster motor harness and connectors for chafing, corrosion, or loose pins
Measure battery voltage and charging system output to rule out low supply voltage during motor activation
Use a scan tool to command the brake booster motor and observe live phase current and voltage data for imbalance
Check resistance and continuity of each phase winding at the motor connector, comparing U-V, V-W, and U-W readings
Inspect and clean the motor and control module ground points, then retest the circuit under load
If wiring and grounds are good, substitute a known-good booster motor or control module to isolate the faulty component
Clear the code and perform a road test with brake assist events to confirm the repair and verify no pending return

What most technicians miss on C0586

A stored C0586 can be set by a momentary voltage dip during engine cranking, so always check for a weak battery before condemning the booster motor.
The phase U-V-W circuit is sensitive to connector pin tension; a pin that backs out slightly under vibration can cause this code without any visible wire damage.
Some vehicles set C0586 when the brake booster motor is commanded during a self-test and the module sees an unexpected current spike, even though the motor still provides normal assist.
A failing brake pedal position sensor or brake switch can cause the module to command the booster motor at the wrong time, triggering a phase performance fault that looks like a motor problem.
After replacing the booster motor or control module, some platforms require a calibration or learn procedure; skipping it can leave C0586 stored even with good hardware.

Can I keep driving with C0586?

If the brake pedal feels normal and the warning light is the only symptom, you can drive cautiously to a repair shop, but avoid heavy braking or towing. If brake assist is reduced or the pedal is hard, stop driving and have the vehicle towed, because stopping distance increases significantly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.