Pressure Isolation (Pressure Maintain)
The electro-hydraulic control unit is activated when the brakes are applied.
If the information from the wheel speed sensors indicates excessive wheel deceleration (imminent lockup), the first step in the anti-lock sequence is to isolate the brake pressure being applied by the brake pedal.
The microprocessor in the coil integrated module sends a voltage to the coil to energize and close the isolation valve.
This prevents any additional fluid pressure applied by the brake pedal from reaching the wheel. With the isolation valves closed, unnecessary increase in the brake pressure is prevented.