How to find shorted to high/ low source voltage ?

[alborz]

Voltage above/ below normal or shorted to high/ low source
This is what I get on my ISX could codes
Does this mean the engine wire harness is somewhere has a cut and has a contact to the frame or another wire? I know the sensor are good since I have change them and still get the fault codes.
Where are the common spots that the wiring might go bad or cut on engine or truck?
Many thanks in advance