An update. I was going down the wrong path on thinking this was all a low voltage problem.

I went over the wiring diagrams and found that there is a 30A fuse located in what they call the Engine Electronics Fuse carrier, which is located under the ECM cover, which is located just under the windshield at the right rear of the engine compartment (lots of fuses on this car, behind the glove box door, in the cargo compartment in the rear, and now a small block of five 30Am fuses in the ECM carrier. Fuse #3 is for the oxygen sensor heating circuit.

After some disassembly to get to it, I found that #3 fuse was blown. I replaced and it blew again, so obviously I have a short. Could be one of the 4 O2 sensors or in the wiring harness from the ECM to the sensors, so I am now trying to chase that down. Once that fuse blew, the entire O2 sensor heating circuit was out, both left and right exhaust banks, so I got the P0030 and P0050 codes for the circuit problem, and then all the other codes on low voltage (no voltage in this case).

Wish me luck as I hope to chase out the short location and get this solved. Hopefully, its one of the oxygen sensors shorted and brought the circuit down. Will know the weekend if I can get to work on it.