Filling pulse
When TCS modulation starts, a "filling pulse" is generated, which means that a small amount of pressure (same for both wheels) is built up in the wheel cylinders for both driven wheels irrespective of the wheel for which modulation with braking will occur. The pump starts, the pressure relief valve closes and the pressure increase valve opens (pre-determined amount of time).
The inlet and outlet valves in the valve block are in their rest positions, i.e. the inlet valves are open and the outlet valves are closed.