What it means
The brake control module monitors how quickly system pressure responds to a command. It sets this code when the measured pressure rise or change is slower than the allowed response time.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
The brake control module monitors how quickly hydraulic brake pressure changes after a system command. C004D sets when measured pressure responds more slowly than the allowed time, pointing to a possible hydraulic restriction, weak pump, air or low fluid, or a pressure-sensing fault.
Common causes
Most likely first.
- Weak or failing hydraulic pump
- Restricted hydraulic passage
- Low brake fluid or air in the system
- Pressure sensor or wiring fault
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Read freeze-frame data and pressure response information to see when the slow response occurred and whether it followed repeated ABS or stability operation.
- Check brake fluid level and inspect the hydraulic system for leaks before operating or testing it further.
- Inspect accessible hydraulic pump, valve, pressure sensor, and wiring connections for damage, corrosion, or loose fittings.
- Compare commanded and measured pressure during the manufacturer's prescribed test, checking sensor signal and wiring for a delayed or implausible reading.
- If sensor circuits are sound, test pump operation and hydraulic passages for restricted flow or air using the manufacturer's procedure.
Common fixes
- Correct low fluid and repair any leak; bleed the system if air is confirmed and the manufacturer specifies bleeding.
- Repair a damaged pressure sensor connector or wiring fault.
- Replace a pressure sensor that fails the specified response test.
- Repair or replace a weak hydraulic pump or a restricted valve or passage confirmed by testing.
Can I keep driving?
Brake pressure is responding too slowly, and ABS or brake assist may be limited. Avoid driving if the pedal feels abnormal, braking is delayed, or a warning indicates a hydraulic fault; arrange prompt inspection because braking performance may worsen.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.