Unfortunately my voltmeter finally gave up the ghost. I was considering pulling the wheel and grounding and plugging in a new WSS hub and turning the ignition on and see if the codes go away before doing the full install if that would work.

What sucks is I bought and replaced the one I thought it was but turns out it was a list of error codes on another site that only went up to 1999 and said "C1234 is passenger front" my fault for not reading better but still on the learning curve on having a computerized car

I'm curious as to why so many codes to begin with. I'm wondering if he has an issue with a PCM, BCM or the data bus?

I would mention this sucker has some major water leaks into the trunk and rear floor board as well as battery box(drilled a small hole so battery isn't marinating in water anymore but back floor board stays soaked in any rain).

I don't know where all the grounds and electrical components are stashed yet so thought I better mention the moisture.

Today out of the blue I started getting "door ajar" warnings and dinging from rear doors and for no reason other night the alarm went off and last night the interior lights came on when driving down the road (could be a bad door sensor but I am suspicious because the left and right rear going out at the same time is a pretty slim chance making me wonder)

Car still runs great but mileage has fallen of a few MPG'*

I'm with mike on this one. There is way too much going on at the same time.
Water leaks are quite common with that car. If you look around you will find numerous threads mentioning the same leaking issues.

It would be easier to tell you what ISN'T leaking ha ha. Yes Sir, seen the threads just need some warm weather to tear it all apart and go after them.

Do you think it would be worth buying a used "PCM,BCM or data bus" and see how that goes?

They aren't that much off say a low mile junker are they?

Got to ask what a data bus is?

PCM is the main brains (computer) and BCM is brake control Module correct?

I would start here, maybe the PCM is just mad over a bad connector. How long you had the car? Codes all come at the same time? Was the car sitting for any long period of time?

Yes, it sat for a long time and when I got it the codes were already there so not sure if there was some catastrophic electrical glitch that manifested them at once or sitting around in a very humid leaky interior has attacked some electrical or what.

Like I said though the car runs great other than half boost just trying to go down that checklist and beat the gremlins

Not at this time, but its a possibility in the future because I don't like 2 of those codes.
C1298 PCM malfunction
U 1255 loss of class 2 communications


Data bus is a physical communication line between all the modules in the vehicle. And there a many modules. PCM, BCM(Body Control Module) Door Modules, Alarm/Theft Module, OnStar, Instrument cluster, Stereo, DIC, I could go on.

I would do as Justin suggested by inspecting/cleaning all grounds between the PCM and battery. If you don't have a OBD scanner, might I suggest even getting a pocket scanner just to reset codes.

if the bus was intermittently shorted to chassis with water it would give a ton of codes too. but the engine codes wouldnt be on the bus they have direct conections to the pcm. so either your pcm has a problem with power/ground or something internal(last) and you have a different issue with water taking out the bus. or maybe just all bad grounds, they dont like to sit or get wet. on a car thats got so many different systems i would clean all the grounds

and fix the leak;
https://www.gmforum.com/2000-2005-90...-water-297561/