Two quickies...

I have a 2017 Chevrolet Express van 2500 that I just purchased.   Feel free to flog me for it but please note I've already beaten up on myself pretty hard about it and it's the primary reason that I've come here.  I'm tired of getting taken advantage of by liars.  I have a 2007 awd Savanavan I dearly love but forced with replacing another transmission for the one I just replaced with 500 miles on it or getting a new van I went with the Express van which runs absolutely great.  A check engine light and an oxygen sensor code had me pretty nervous but with a upside oxygen sensor being the culprit I was assured...need I say more?  To make matters worse once I was home and with the neighbors scanner suddenly a transmission communication code came up.  Big surprise... How easy they are to erase.  I've got no questions about all that yet I've watched the videos bought the book and I'm still deep enough and study to know that I can't quite ask any questions yet. 
The no TCM signal may come from a couple of splices that I found just this afternoon before it started raining.  The TCM is internal and repair logs (nomenclature still being a huge obstacle) indicate wiring issues with that unit ad that to disturbed wiring I have found your videos have convinced me that dropping the transmission straight away is not wise.  
My question is with regard to programming.  I noticed in several of your videos you recommended a battery maintainer was dire consequences if ignored.  I had a upside number One Bank O2 sensor code that I needed to track also. Believing what I was told I've already replaced all four sensors with 200,000 mi on it it wasn't a big enough expense to worry about and something I could easily do.  As it turns out the battery that came with it was crap also   Having to replace the battery I obviously had to disconnect the power to replace it with a new battery and now I've noticed that I've lost the bank 2 upper sensor.  I suspected as soon as I replace those sensors that it was a wiring or a programming problem with the computer. Now that I have replaced the battery, I noticed it was a little difficult to start, ran a little rough to start with but seems to be okay now.  I don't know if a way that I could change a battery and not lose the charge.  Stop laughing I can hear you from here, I'm sure there must be a way but I don't know it.  I keep a trickle charger on it all the time now to maintain the new battery as well as the constant charge.  What are consequences could have resulted from the loss of power in the change.  I have followed and now no more about fuel trim and how oxygen sensors, no make that switches, operate in tracking a wiring problem are such that I'm not too worried about my abilities there but when it comes to programming... There's one shop in town that I really trust.  There's one shop in town that has a really great reputation, I'm not sure I'm capable of trusting anything or anyone at this point in life, but it takes at least 2 weeks to get in there to see him.
Should I make an appointment? 
I'm afraid of these computers to be honest with you I know so little about them.  If there's every good chance that I've caused a programming problem by disconnecting the power I can make an appointment now while I'm tracking down some other issues. 
I don't really need a pat on the back at this point I haven't worked hard enough yet but you could ease my mind about this programming.
Thanks ahead of time.
(This question was a direct result of something you said on one of the videos or I would not have asked, I would have done the research through the form here.  I have yet to unsheathe my sword against that monster yet... The videos alone have been foe enough)
)

The battery maintainer is to keep voltage stable while programming modules, as you are aware. Programming would be carried out if for instance you had to change a computer. Then you would require software from GM, a programming tool and a laptop to configure the software to your vehicle. It doesn't sound like you did any programming while changing the oxygen sensors, so I think you dodged the bullet in that regard. The danger would be corrupted software if the module lost power during the programming, which would likely result in a no start condition, configuration errors or possibly a bricked computer. Not maybe running a little tougher than normal or a problem with a single sensor.
As for the transmission code, it's quite normal to encounter communication codes in modules that have no problems. I wouldn't immediately suspect a problem with the transmission just because there was a history communication code of it wasn't accompanied by a tangible drivability issue with the transmission.
Don't be shy to ask anything, every body here is friendly and helpful

Wow... I'm a little blown away by the speed and thoroughness of your reply BUT, I'm not a bit surprised judging by what I've already seen on this website. I can't speak for professionals but for a layman or young beginner, this resource is truly priceless. You should be very proud of what you are doing here.With that said...I'm relieved that ignorance didn't let me make a bad mistake. It didn't makes sense to me that simply changing a battery could result in corrupting a programming for a computer especially when one considers the total lack of quality in the batteries that we can purchase today. I understand more than I let on here I suppose but it's the programming issue that will remain a problem for me, at least in the early stages of learning here. There's no point in purchasing the hardware necessary to do that level of programming until I get to the point where I have the training to use it.
Why buy an airplane before you can fly?
All the other tools mentioned I already have. My scanner is the top of the bottom line units available at harbor freight. I can hear more laughing...bur harbor freight does offer some affordable alternatives for non-professionals who need tools or materials that won't be used in the same way that a professional would require.  (Money has not been an object for me professionally when meeting a tool that I know I'm going to use and rely on, I'm a long ways from calling myself a professional here, at this point) My scanner has graphing capabilities but from seeing your videos are very limited in scope.
I endeavor to preserver in spite of my hardwear limitations.
My biggest relief is in your reinforcing the suspicions of a local tranny specialist whio suspected a bad code. What I find confusing is if the code is telling me it has no communications with the transmission, yet the transmission is functioning perfectly where is the problem?
I'm a little hypersensitive about transmissions after what I've been through with my 07 Savannavan. The way I see it, correct me if I'm wrong, but codes are used not only to point out an actual problem but something has triggered them indicating a future problem or a current problem that hasn't come into fruition yet. I'm headed out now to track down what I think might be causing the problem which is a wiring issue. I've also learned from you the importance of thoroughly inspecting the entire path that any signal takes in analyzing a problem. Right away I noticed that the insulation around the harness leading to the transmission plug at the transmission was loose and all pulled back, a red flag telling me someone's already looked into this problem already.
And then, late yesterday afternoon, I noticed that the wiring coming out of the back of the fuse block underneath the front seat, the body module I believe it's called had a couple of plugs which had some unhealthy looking splices. I'm going to stop saying that I learned this from the videos because basically everything I know to date has been learned from your videos.
Until now, when I saw a wiring diagram I might as well been looking at a plate of spaghetti. After a closer more learned inspection I noticed that the two wires that were spliced were both the tan wires that the wiring diagram says lead to the transmission (TCM). This is exciting for me because I feel like a hound dog that's been running around all night who has just put his nose on the scent of a big fat raccoon. I don't have the raccoon yet but at least I'm on his trail now.
The very first thing I did before I did anything else was to check every fuse in the vehicle... Process of elimination is a big part of diagnostics if not the biggest part of diagnostics. When I saw those spliced wires and read your reply today my ears perked up because I knew I was on the scent and then all the time I've spent in the last week looking at videos and learning about the huge holes I had in my basic knowledge about all things electrical was actually starting to kake a lot of sense. It's a huge shot of confidence that has eluded me for years.
Thanks again, for not just me, but for how much your efforts are helping countless other people with their automotive problems.
Back to the hunt..bow wow! (Hugely interesting was the epiphany in learning the 02 sensor creates it's own current, the wiring diagram really had me wondering? Understanding circuitry still a very high and steep learning mountain for me but one I feel comfortable attacking now that I have a reliable guide)
catman...ttyl

Do you recall which transmission code you found, specifically? And in which module it was stored? If you scanner has the ability to do a complete vehicle scan and save/export the results, that'd be even better.

I'm with Noah about the communication code. It's pretty common for newer vehicles to have history communication codes stored in various modules, in my experience. I don't get excited unless I have a symptom/complaint to go along with them.

I'll pass your kind words up the ladder to Paul Danner aka ScannerDanner .
He pops on the forum here and there and he would appreciate your enthusiasm.