What are the common causes of C0591?

Low current draw in brake booster motor A phase U, V or W. High resistance in the motor A phase wiring. A partially open motor A phase winding. A corroded motor A phase connector adding resistance. A weak phase driver in the brake booster control.

Check the brake booster motor A connector for corrosion. Measure resistance across each motor A phase pair. Test the motor A phase wires for high resistance. Check the motor A supply voltage under load. Replace the brake booster motor if a phase winding is weak. Clear the code and retest.

C0591

Brake Booster Motor A Phase U-V-W Current Low

System: Chassis control (C code)
Lamp: Check Engine Light
Category: Chassis

What it means

C0591 means Brake Booster Motor A Phase U-V-W Current Low.

Check these first

Low current draw in brake booster motor A phase U, V or W
High resistance in the motor A phase wiring
A partially open motor A phase winding
A corroded motor A phase connector adding resistance
A weak phase driver in the brake booster control

What to do next

Check the brake booster motor A connector for corrosion
Measure resistance across each motor A phase pair
Test the motor A phase wires for high resistance
Check the motor A supply voltage under load
Replace the brake booster motor if a phase winding is weak
Clear the code and retest

Look up another code

Code or symptom

Enter a full code or a symptom. Press / to search. How to read a code

Type a code above, or start from a symptom or a common code.

Updated

Generic SAE J2012 definition. Last updated 2026-10-10.