Crazy "KEY error" situation, stumped - 2008 C30

[BOOSTSTARZ]

This will be a decently long post just a heads up, new to this forum and volvos but not cars AT ALL. I've ran shops for the last 13 years, im not an automotive genius but I'm far from car dumb... on to this ridiculous story of my VERY FIRST VOLVO...

So I purchased this car knowing it had a "sleight" starting problem. Did my research and wanted a C30 for a few years now so pulled the trigger being confident I could fix it quickly and get this car half priced...BOY WAS I WRONG. So when I bought it it ran great, still does, but would throw the " KEY ERROR" message once or twice a day. After a week, it went downhill fast, only starting after battery unhooked for 1-3 days, so I replaced the SCU and it did nothing, took the ECU off, cleaned connections not that it looked like it needed it and put back in. Took CEM out, no corrosion, took board out of casing, no corrosion, cleaned all anyways and out back. Still nothing. Took it to the dealer and now after a month I have it back, this fixed nothing and was a waste of time. At first they thought it was the SCL and replaced it, nothing. Spent 3 weeks messing with it to just be stumped the whole time, stating there was no communication between CEM and ECU, software update did nothing. Then one day they put a battery charger on it and it started a few times, mind you battery was tested by me and them a dozen times and is putting out over 12v. After that it lost comm again and asked for 7 hrs of wiring diag time. After another week, they again were nowhere and the tech bumped the dangling SCU with his hand and it starter up, several times for 2 days. Again, then back to nothing. So I brought it back to me (my shop) and it seems to be starting randomly, few times throughout the morning but not afternoon, and I am so frustrated its not even funny, I'm ready to give up but I do not want to its a fun car, exactly what I wanted, im reaching out for help, someone please help me lol. Thanks in advance.

P.S. quick recap...battery good, Cleaned CEM and ECU. Replaced SCL and SCU... about to give up...Also will throw random SCL error but once every few days...

[highmiles]

My car is a 2001 S60 T5, so probably less complicated by some factor. I am currently working through a starting issue as well, not likely related to what your are dealing with, but understand the frustration. My experience has been that most of the error messages are likely to lead to chasing your tail. If the car, when running, runs well and without codes my sense is that generally things with the control units is all good. I would suggest checking every ground in the car for tight clean connection. Then move on to looking for a cut wire creating an intermittent short.
I assume that unlike my car, yours won't crank at all when getting the key error?
Keep at it, you will figure it out.

[BOOSTSTARZ]

Exactly it will not, and yes when running it runs like a top! That is what I'll be doing this weekend is wiring and grounds, it was in a small accident in its past before I bought it so I have a general area to look. Also I agree, that computers should be perfectly fine, I don't see how when running it be perfect with no codes if it wasn't a connection type issue. Thanks and good luck to you too bud.