[Qui-gon]

I would say you have a wiring problem. I posted links to the sensor pdfs on this site a while back, if you do a search they should come up.
The water temp sensor is on pin 4 ECU and the other end is on sensor ground pin 22 ECU. The resistance of the water temp sensor is 3k ohms at 25 deg C nominally and has a negative coefficient (resistance decreases with temp)
The battery volts are read off the switched input to the ECU on pin 26 which is the switch 12v line from the ignition switch.
My guess is the codes are a grounding issue to the ECU. It must be intermittent otherwise it shouldn't run.
You don't state in your post if it runs and what the dealer did to it
Hope that helps