Brake Fluid Solenoid Valve Relay: Description and Operation

The solenoid valve relay is actuated by the control unit (closes) as soon as the control unit receives voltage from the alternator (D+/terminal 61).

As soon as the relay has closed (picked up), battery + (terminal 30) is present at the valve coils of all solenoid valves of the hydraulic unit.

If the ABS or the TC (ABD) begins controlling, the control unit applies negative potential to the appropriate valve coil of the valve to be controlled at the appropriate wheel.