Shuttle Valve Switches
The ABS modulator houses two shuttle valves. The valves are actuated when brake pedal pressure is applied via the master brake cylinder. The shuttle valves have a micro switch attached to them and a set of resistors located between them. The resistance of the circuit controlled by these shuttle valve switches will change depending on the position of the shuttle valve. With no brake pressure applied, the current flows through all three resistors.With one switch closed, the current flows through two of the resistors. And when both valves are closed, current flows through one resistor. This gives a circuit resistance of approximately 3 K, 2K and 1K respectively. The signal from the shuttle valve is used by the ABS ECU to detect the correct operation of the brake master cylinder and the integrity of the braking circuit.

Shuttle Valve Switch Failures
The bad news is that shuttle valve switch failure messages are more or less a death sentence for the ABS modulator. The failure may start off in the begninning as a intermittent reoccurance but will eventually progress into a full blown permanent failure. I would first recomend following the check list outlined in the repair options below; make sure that the failure is not an electrical connection failure. The next course of action is to then clear the fault and take the vehicle for a test drive. If the fault returns, then consider installing the Shuttle Valve Switch Kit (200 USD). The shuttle valve switch kit is unlikely to repair the problem, but it is a relative inexpensive repair option. If the fault continues to return, then the replacement of the entire ABS modulator assembly is required. This replacement can cost roughly 2000 USD and should be performed by a trained Land Rover mechanic.