What it means
Fault on master cylinder cut-off valve — used in brake-by-wire systems to isolate the master cylinder during normal electric boost.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
In some brake-by-wire systems, a master-cylinder cut-off valve isolates the master cylinder during normal electric boost. The brake control module monitors the valve's electrical operation and response; this code indicates a valve or control fault that can affect the intended braking mode.
Common causes
Most likely first.
- Cut-off valve stuck or mechanically binding
- Valve coil open or shorted
- Damaged wiring or poor connector contact
- Hydraulic control module fault
Symptoms
- ABS warning light on
- ESC/stability control may be disabled
How to diagnose it
- Read brake-module freeze-frame and live data for cut-off-valve command and feedback, and check for related hydraulic or power-supply codes.
- Inspect the valve connector and nearby harness for loose pins, corrosion, fluid contamination, or damaged insulation.
- Check the valve circuit fuse, supply, ground, and wiring continuity against the manufacturer's specification.
- Test the valve coil and command response using the manufacturer's procedure, checking for an open, short, or valve that does not move as commanded.
- If the circuit and valve pass, follow the service procedure to assess hydraulic binding and the brake control module.
Common fixes
- Repair a loose, corroded, or damaged cut-off-valve connector or harness.
- Replace a failed fuse after correcting the cause of the fuse failure.
- Replace a cut-off valve with a confirmed electrical or mechanical fault.
- Repair the hydraulic control module fault if the valve and circuit test correctly.
Can I keep driving?
Treat this as a brake-system fault: have the vehicle checked promptly and avoid driving if pedal feel or braking response is abnormal. The system may limit brake-by-wire, ABS, or stability-control functions.
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.