Thought I'd bump this up I found this and other Dodge forums a big help in solving this issue with my 2001 1500. Although if you are searching for a for sure fix you will not find just one because the "no bus" can be caused by sooooo many things. I do have a pretty good idea for trouble shooting that I developed over the last couple of evenings.
Here goes, My truck would only crank, no fire, no codes, only a no bus fault on the odometer, the only hint that this might be on the horizon was a couple of weeks ago it would not start after running to town for lunch, I cycled the key and it started right up,this time no amount of cycling the key or even pulling the battery ground helped.
Second, all mu gauges seemed to work, they all passed the hold down odometer reset while cycling the key test. ( hint #1 fuel guage read dead empty and I knew darn well I did not leave it empty).
So start here, with the key in run pull off the air cleaner and unhook the throttle position sensor plug, you should have one pin reading 5 vlts, most likely you won't because there is possibly a shorted sensor so unplug the crank sensor, cam sensor,map sensor, and a few tranny sensors that run off this 5 vlts. if you see the voltage come back up you found your issue. None of this worked for me so...
Next step pull the left and center plug on the pcm, did you get the 5 vlts back? If so You have some other stuff dragging the pcm voltage down, like egr solenoid,and the other emmisions solenoid I forget the name.
None of that worked for me soooo now to the gritty stuff, get the multimeter and pull the driver's side plug off the pcm, check pins #31 and #32 to chassis ground should get less than 1 ohm. If not check your grounds, there's plenty, you just have to crawl around and do the dirty work, no easy fix there.
Next check pin #22 it should have battery fed 12 vlts. if not you have a bad wire almost for sure or bad connection at the main fuse box, so aptly named "Power distribution center"or PDC. If you have 12 vlts go to pin #2 this is "switched 12 vlts." turn the key to run, not off, or acc. If you don't have this or if it is lower than say 10 vlts. you have an issue. This is where it can get tricky, this 12 vlts. is fed fron the PDC to the fuse box #9 fuse on the drivers side of the dash and back to the PDC and also distributed to an array of items, any of which can be shorted fuel pump. sending unit, ASD relay ect. ect. At the PDC there is a large multi-pin plug about 2 inches square and held down with a pathetic screw that will not really tighten down, here is where the switched 12 vlts to the pcm is finally distributed to the harness. Here is where I found my problem, a green wire black stripe (there are several of these remember it goes various places) one of them goes into the bottom of this large multi-pin plug, you must take apart the PDC (i.e. large fuse box in engine well) to get to this. My wire was broke (almost) down in the harness about 3 inches from the plug. This is why my fuel guage did not show the proper reading also I never heard the fuel pump run as I turned the key on, there may be other symptoms.
Although this fixed my problem I thought of the next step, if you get your switched 12 vlts. and you still have the no bus error check the same far right (drivers side) pcm plug figure out which wire is going to pin#17 and clip it about 3 inches from the plug, and test for your 5 vlts, if you have it after you clip it it's very likely your pcm is good if you don't it's prolly a goner. If once you splice then ends back together (leave room to push in a test probe) you no longer have 5 vlts you still have a short.....somewhere.
Sorry to run on but all the other posts while great help didn't really cover the power going to and coming from the PCM, I hope this helps!