What am I looking for in checking my 5 volt bus for proper operation? Are we talking just a voltage test? Fuel gauge, coolant temp and transmission shifting have been odd.

Yep, 5 volts is 5 volts. Have you by chance checked the alternator for AC leakage?

The ecm sends 5V out to sensors transducers ect and it looks for variances or fluctuations in the return signal which should always be less than 5 v if things are working properly, when testing things make sure of signal wires and return voltages if checking at components, this can throw off a lot of people when troubleshooting thinking they have an issue by not seeing 5v on the ecm return wire.

Alternator noise is within normal range. Where is the 5 volt bus located? Is it part of the main fuse panel? What's it look like? I've done searches and have found nothing on testing it or locating it.

It is actually called a Can Bus "Controller area network" that came along around 1996 when OBDII became standard and is what the ecm uses to communicate with most electronic components, it is a small 5 volt wire that runs from the ecm to almost every electronc component, sensor and gauge and back to the ecm, so to answer your question about half the wires in the harness are related to the bus.

If you have an issue with the Can bus circuit it will throw a code for whatever circuit it is in or major issues all together, the issues come when you have a bad connection or component not doing what it is supposed to some of which may or may not set a code all depends on what protocol is set via the OEM on that. 

The 5 volt bus has nothing at all to do with the CANbus at all. The CANbus (Or variants of, Eg: SCI, J1939) communicate between different modules (Eg: ECM, PCM, Air bag, Antilock brakes).

The sensors get 5VDC from the ECM & return a signal voltage. They are still ALL analog.

I will get you specific test points later after looking at the schematic.

 

Ed

Thanks for the correction Ed, heavy equipment is behind automotive in making all electronic controls use the same system but are all just trying to find common ground as automotive industry did but have a long long ways to go yet. I was intertwining the two as they are in my world on lots of heavy equipment yet but not all and mixed up the two systems.

 

Think of automotive Can bus at a sort of ether net system connecting all the main ecms; ecus, and other computer controllers together.