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DTC codes / C05xx · Brakes, steering and suspension / C0571

C0571Active Brake Assist Performance

C0571 indicates that the vehicle's Active Brake Assist system has detected a performance fault, meaning the system cannot reliably apply braking force automatically when it determines a collision risk. The computer monitors wheel speed, brake pressure, yaw rate, and steering angle inputs and sets this code when the measured response does not match the commanded brake assist request within an expected time or pressure window.

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

Symptoms you may notice

  • Active Brake Assist warning light or message displayed on the dashboard
  • Traction control and stability control warning lights may also illuminate
  • The system may disable itself and show a message such as 'Brake Assist Unavailable'
  • Brake pedal may feel firmer or softer than usual during normal driving
  • Often no symptoms besides the warning light, with normal braking performance otherwise
  • Intermittent warning that appears during certain driving conditions such as low speed or turning

Common causes, most likely first

  1. Low brake fluid level or air trapped in the hydraulic brake system
  2. Faulty wheel speed sensor or damaged sensor wiring at one or more wheels
  3. Weak or failing brake pressure sensor or master cylinder pressure switch
  4. Degraded brake booster or vacuum supply issue affecting assist performance
  5. Corroded or loose electrical connector at the ABS/ESC control module or brake pressure sensor
  6. Software calibration issue in the ABS/ESC module requiring reprogramming
  7. Internal fault in the ABS/ESC hydraulic control unit or pump motor

How to diagnose and fix it

  1. Check brake fluid level and inspect for leaks at calipers, lines, and master cylinder
  2. Scan all modules for related codes and freeze-frame data to identify which input signal is out of range
  3. Inspect wheel speed sensor wiring and connectors at each wheel for damage or corrosion
  4. Test brake pressure sensor output with a scan tool while applying the brake pedal and compare to expected values
  5. Perform a brake system bleed if air is suspected, following the manufacturer's sequence
  6. Check brake booster vacuum supply and booster operation if assist feels weak
  7. Reprogram or replace the ABS/ESC control module only after all hydraulic and electrical inputs are verified good

What most technicians overlook on C0571

  • A low brake fluid level from worn pads or a slow leak can set C0571 without any visible leak under the car, so always check the reservoir first.
  • Wheel speed sensor signal dropouts at low speed are a common cause that does not always set a separate wheel speed code, so live data review is essential.
  • The code can be stored by a momentary voltage drop at the ABS module during engine cranking, which is why checking battery and ground condition matters.
  • After any hydraulic repair, the brake pressure sensor must be recalibrated or the module will continue to command assist incorrectly and reset the code.
  • A misaligned steering angle sensor or yaw rate sensor can make the system think a collision is imminent and trigger brake assist performance faults.

Can I keep driving with C0571?

The vehicle remains safe to drive with normal braking in most cases, but Active Brake Assist will not function and the system may disable stability control. Avoid situations that rely on automatic emergency braking and have the fault diagnosed promptly, especially if the brake pedal feel changes.

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.

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