My G35 has had a bad electrical problem for the time ive had it. I have checked the NDS 2 software and figured it to be the 5 volt reference. I have checked the reference using a O-scope and found that when the car is not cranked, the 5 volt is perfectly good, straight line clean signal. After cranking the car the signal goes to crap, and becomes a square wave. The APPS was the culprit that I originally had. The voltage from the APPS was fluctuating between the normal 0.75 volts to anywhere from 0.2 volts to 0.5. We have changed the APPS and then discovered the 5 volt was bad. I sent the ECU to get repaired for unrelated matters. Images listed are the O scope readings.

 

Figured it out. It was a 5 volt wire that had been cut into by a pulley. Lesson learned, always check your clearances.

 

You went deep into the diagnostic too!