It's digital talk. Low ref is not exactly ground more like 0 volts. 5V ref is exactly 5 volts. With those parameters you know exactly what the signal should be i.e. between 0 and 5, but really .2 to 4.8 because of resistance in the circuit.

In a digital circuit "on" is 5 volts "off" is less than 5 volts (usually 0 volts)

 

Ok well I have decided just to replace the damn thing and see if that is my problem. I could have fried it. I plugged in the connector to the fuel rail to the throttle body and the throttle body to the wiring harness. The other day and I tried to start the car and when it didnt start that's when I realized I had them backwards.