Hi Alan,

I would like to explain how Prius's brake system is implemented since the FEH is licensed by Toyota's THS system.

Basically, the brake system is brake-by-wire.
Your brake force is received by the brake pedal stroke simulator converting to an electric signal.
The skid control computer receives the signal including signals from each four wheel speed sensors, yaw-rate-sensor, G-sensor and steering-sensor, then it sets the regenerating braking force and friction brake force.

The vehicle has oil pressure accumulator for the friction brake and each wheel has solenoid valves for that.

Therefore, your brake input will cause regenerating brake first, then goes to friction brake if you need more braking force.

There is a fail-safe system.
If the vehicle lost 12V power, there is an electric power back-up supplying by super capacitor.
If the vehicle lost everything, your brake force applies mechanical force to front brakes.

Please to refer to following page...
http://www.toyota.co.jp/en/tech/envi...s2/system.html

Regards,
Ken@Japan