Hi,
What you are doing in the first diagram is scaling the output of the sensor to make it suitable for the factory controller.
That is you did using a serial type system.
The second diagram you want to use SHUNT LOAD to scale the output for the factory controller so you don't have to open circuit the signal wire.
As @aarg has pointed out what is the output impedance of the sensor?
Can you tell us your electronics, programming, Arduino, hardware experience?
to reduce a dynamically defined percentage of the voltage.
What is the characteristic you need to apply to the 5v sensor signal to make it suitable for the factory controller.
Do you just need to reduce the signal by a fixed percentage?
Thanks.. Tom... 