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DTC codes / C05xx · Brakes, steering and suspension / C0593

C0593Brake Booster Motor B Phase U-V-W Current Low

The anti-lock brake system (ABS) control module monitors the three-phase current feeding the brake booster motor and has detected that the current in one or more of the U, V, or W phases is lower than expected for the commanded output. This indicates a problem in the motor circuit, the motor itself, or the module's current-sensing feedback, and the module stores C0593 while disabling the electric brake booster assist.

SystemChassis
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaBrakes, steering and suspension

Symptoms you may notice

  • Illumination of the ABS, traction control, and brake warning lights on the dashboard
  • A hard brake pedal with noticeably increased pedal effort because the electric booster assist is disabled
  • Reduced or absent brake assist, especially at low engine speeds or during the first few pedal applications
  • A whining or grinding noise from the brake booster motor area when the brake pedal is pressed
  • The vehicle may enter a reduced-power or limp-home mode with limited braking performance
  • Often no symptoms besides the warning light if the fault is intermittent or only affects one phase at low load

Common causes, most likely first

  1. Damaged or corroded wiring harness between the ABS module and the brake booster motor, including chafed wires or a loose connector
  2. A failing brake booster motor with worn brushes, shorted windings, or an open phase winding
  3. High resistance in the motor phase connectors or ground circuit causing low current feedback
  4. A faulty ABS control module with a degraded current sensor or driver circuit for the booster motor
  5. Low system voltage or a weak battery that prevents the motor from drawing normal phase current
  6. Moisture or contamination inside the motor connector or module connector causing intermittent phase current loss

How to diagnose and fix it

  1. Verify battery voltage and charging system output, then clear the code and test-drive to confirm whether C0593 returns immediately or only under specific conditions
  2. Inspect the brake booster motor harness and connectors for corrosion, chafing, loose pins, or signs of overheating, and repair any damaged wiring
  3. Measure resistance across each motor phase (U-V, V-W, U-W) at the motor connector and compare to the manufacturer's specification to identify an open or shorted winding
  4. Check the motor ground circuit and power supply for excessive voltage drop under load using a multimeter or oscilloscope
  5. If the motor passes electrical checks, substitute a known-good brake booster motor or perform a module swap to isolate the fault to the ABS control module
  6. After repair, clear codes and perform the manufacturer's required brake booster calibration or ABS bleed procedure, then verify the warning lights stay off during a road test

What low phase current really means

  • A low current reading on one phase often comes from a poor connection at the motor connector rather than a failed motor, so inspect and clean the terminals before condemning the booster assembly.
  • The ABS module may set C0593 when system voltage drops during cranking or under heavy electrical load, so a weak battery can mimic a motor fault and should be ruled out first.
  • Some vehicles store C0593 only as a history code after a single low-current event, and the code may never return if the connector was disturbed during unrelated service.
  • A brake booster motor with a partially shorted phase can still produce assist and pass a simple resistance check, so a current waveform or bidirectional scan tool test is more reliable than a static ohm reading.
  • Replacing the ABS module without checking the motor phase resistance can leave the new module with the same low-current code if the motor is the true cause.

Can I keep driving with C0593?

Do not drive the vehicle if the brake pedal is hard or brake assist is clearly reduced, because stopping distance increases significantly. If the only symptom is a warning light and the pedal feels normal, limit driving to a short trip to a repair shop and avoid heavy traffic or high speeds.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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