Module to module communication

Sometimes a module will send out a 5v reference to a sensor.  Usually a module recieves battery voltage to "power up" a module. My question is: where does the 5v come from that the module sends out to say a hall effect sensor. Does the module step down the 12v supply to 5v? Or does the pcm directly supply 5v reference,  as well as the 12v supply, to the module?

I know that there is ususally only 1 regulator in a vehicle.  And a hall effect will require a steady 5v ref. So in order for the hall effect to recieve a regulated/steady 5v, wouldn't the pcm and the regulator, directly supply the 5v ref to a module that uses a 5v ref?

This is in reference to a Isuzu 5.2l diesel that uses a position sensor on the turbo actuator.   

Also, the 5v reference wire has 10.3v on it from the module. How can a 5v reference circuit be elevated for one circuit but the rest of the sensors in the truck have 5v on their ref circuit?

I may have complicated my question previously. I'll rephrase. If the PCM has the only 5v reference circuit/regulator, then how can other modules "send out" a 5v reference?

Your question isn't exactly clear....
There's isn't always one 5 volt reference circuit, and more than one computer can have a 5 volt regulator.

Can I take it on step further? If a module, say the BCM for example, is sending out 5 volts as a reference, then is there a regulator in that module? Battery voltage coming into a module is unstable, correct? So wouldn't it need a regulator to step down the 12 volts coming into the module and for it to be steady? Thank you!

You are correct, the battery supplies modules with 12-14v and the internal 5v regulator converts to 5v for the reference circuit.