What it means
The brake control module monitors pressure in hydraulic circuit D for signs of fluid loss. It sets this code when pressure drops below the expected level or the circuit otherwise indicates a leak.
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 hydraulic pressure in brake circuit D and checks whether it holds as expected. This code sets when pressure in circuit D falls below the expected level or the system detects evidence of fluid loss; circuit D is the specific circuit implicated.
Common causes
Most likely first.
- Leak at a hose, line, caliper, or wheel cylinder in circuit D
- Loose or damaged hydraulic connection
- Damaged master cylinder or hydraulic control unit seal
- Faulty pressure sensor or wiring
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Check the brake fluid level and inspect the master cylinder, hydraulic control unit, lines, hoses, calipers, and wheel cylinders serving circuit D for leaks.
- Save freeze-frame data and compare circuit D pressure readings with other circuit data to confirm when the pressure loss occurs.
- Look for wetness or fluid trails at circuit D connections and components, taking care not to mistake road grime or grease for brake fluid.
- If no leak is visible, inspect circuit D pressure sensor wiring and connector, then verify its signal against the manufacturer's specification.
- Have the hydraulic circuit and control unit seals tested using the manufacturer's procedure if external components and sensor circuits pass.
Common fixes
- Repair or replace a leaking hose, line, caliper, or wheel cylinder in circuit D.
- Tighten or replace a damaged hydraulic connection serving circuit D.
- Repair or replace a leaking master cylinder or hydraulic control unit seal if testing confirms the source.
- Repair circuit D pressure sensor wiring or replace a faulty sensor after verifying the hydraulic system.
Can I keep driving?
A leak in circuit D can reduce braking force and worsen quickly. Do not drive if fluid is low, a leak is visible, the pedal sinks, or braking is weak; arrange recovery.
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.