Code 1635...not to sure

Hello there I bought a code from ebay finally, works great and was wondering now if anyone else can shed some light on code 1635, it says a bad reference wire 1 or a circuit. I looked at the wiring diagram and I think its for the tps switch 5 volt reference which I checked to be ok??? The van does start doing some weird things when this code sets so maybe its the tps itself. Any help would be great
Thanks

The +5V line is having problems somewhere. Either it's being shorted out (frayed wire, poor connector, etc) or the source of that +5V is failing. Since the computer powers that 5V line, you don't want it to be the latter.

OK here goes a theory.. since I'm still chasing a fuel guage and now this 1635...which by the way only acts up when the fuel guage starts to go south, I traced the wires in my new haynes and they end up at the cpu...I'm not saying the cpu is bad yet...I hope but if the sending unit was bad could it possibly short out the 5v ref line? I think i'll unplug the sender wires at that easy connector and see what happens,..
thanks for the info cdru, you've been a great help.