Chassis, generic

C004D Brake System Pressure Slow Response

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

A performance code set when the brake system builds or changes hydraulic pressure more slowly than the control unit commands during an assisted or automated braking event. In electronically controlled brake systems the module commands a target pressure and watches the pressure sensor; if the measured pressure lags the demand beyond a calibrated time or rate it concludes the pump, motor, valves or hydraulic path cannot respond quickly enough. It is a plausibility and timing fault rather than a single electrical defect, and can be caused by air in the system, a weak pump, a sticking valve or a restriction. Automated braking and stability functions are limited and the brake or ABS warning lamp is set. The entry follows the SAE J2012 generic definition and electro-hydraulic brake control design.

Likely causes

Air in the hydraulic system or low fluid
Weak pump or motor performance
Sticking valve or hydraulic restriction

Symptoms

  • Longer pedal travel or delayed assist
  • Automated braking functions limited
  • ABS or brake warning lamp on

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–2,000
Time1–4 h

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

Parts involved

hcubrake pump

Related codes

C004EC004CC0044

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