Firstly, I don't know if this is the right StackExchange, but I will try nevertheless.
Above I posted a picture of the hydraulic circuit of an ESC (Electronic stability control) system (with ABS (anti-lock braking system). Now the upper 4 valves (2 per circuit) are used to autonomously build up pressure (ESC intervention or autonomous emergency brake). Normally the inner valve is open, which leads thought the ABS valves directly into the wheel.
When ESC wants to brake on its own, it closes the inner valve and opens the outer valve ("suction valve"). This way, the path leads through the hydraulic pump and backflow is blocked by additional directional valves (I guess this is how the autohold function is working). By operating the pump, the system can now build up pressure. But since this option is only available circuit-wise, it would put pressure on two wheel at a time. As commonly known, ESC stabilizes a vehicle by braking a single wheel to induce a rotating force countering the instability.
The only possibility I see braking just one wheel is by blocking it with the ABS valve. Does that mean that, even when the driver steps onto the brake pedal, the wheel which is not intended to be braked is completely not brakeable? I dont think this would lead to a good dynamic, since it would have much less pressure than the whhels in the other circuit which are unaffected. Or does the ESC react to this and works like an electronic brake force distribution by temporarily letting fluid flow into the unbraked wheel, so that the pressure in this wheel is regulated to be the same as in the other circuit?