Chassis, generic

C004C Brake Booster Motor A Position Sensor Exceeded Learning Limit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Set in an electric or electro-hydraulic brake booster when the position sensor of booster motor A reports a learned reference value outside the allowed adaptation range. The brake control unit learns the rest and travel positions of the motor-driven actuator so it can meter assist precisely; if the learned value drifts beyond the calibrated window the module can no longer trust the actuator position and stores this code. It points to a worn or shifted sensor, mechanical wear in the actuator or a learning routine that ran under wrong conditions rather than a hard electrical fault. Controlled brake assist is reduced or disabled and the brake or ABS warning lamp is set; conventional braking remains. No code-specific public bulletin was confirmed; the entry follows the SAE J2012 generic definition and electro-hydraulic brake actuator design.

Likely causes

Position sensor worn or shifted
Mechanical wear in the booster actuator
Learning routine ran under wrong conditions

Symptoms

  • Reduced or inconsistent brake assist
  • Changed brake pedal feel
  • ABS or brake warning lamp on

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€250–2,000
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

booster motor a pos sensor

Related codes

C004DC004EC0024

References: patents.google.com, en.wikipedia.org.