C0585: Brake Booster Motor B Phase U-V-W Circuit High

What it means

The brake booster motor B phase circuit voltage is above the expected range. The code alone does not identify whether the cause is the motor, wiring, or control module.

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, with U, V, and W phase circuits carrying the motor drive signals. The control module sets C0585 when a phase circuit voltage rises above its expected range, which can happen if a wire contacts a power source and may limit brake assist.

Common causes

Most likely first.

1. Phase shorted to power
2. Connector pins corroded - high contact resistance
3. Supply wire pinched against B+ source

Symptoms

• Brake or ABS warning light
• Brake assist may be reduced or unavailable

How to diagnose it

1. Use a scan tool to record freeze-frame data and check brake-booster live data and related codes for the conditions when the high-voltage fault occurred.
2. Inspect Motor B's U, V, and W wiring for pinching or chafing where a phase wire could contact battery power or another powered circuit.
3. Check the phase connector for corrosion, loose terminals, or damaged insulation that could affect the signal.
4. Using the vehicle's wiring information, test the identified phase circuits for a short to power and verify continuity as specified by the manufacturer.
5. If the wiring and connector pass, test the motor and control module circuits according to the manufacturer's procedure.

Common fixes

• Repair phase wiring that is shorted to a power source.
• Clean or repair damaged, corroded, or loose Motor B connector terminals.
• Repair or replace a pinched or chafed section of the phase harness.
• Replace the brake booster motor or control module only if testing confirms a fault.

Can I keep driving?

Brake assist may be reduced or unavailable, so avoid driving if pedal effort or braking response has changed. Arrange safe transport for diagnosis if braking feels abnormal; continued driving can make stopping harder.