Well, Scanned Mother-in-Laws TB this morning. The code turns out to be P0606, darn, not what I wanted to see. Those idiots at the steelership can't even give me the correct code. She explained to the service adviser I couldn't find the 6046 code they were faulting online, they stated only GM would know what it is, OK...P0606 is Internal Processor Fault, she told me it's only happened once, and like I stated earlier, the check engine light was only on for one cycle. At this point this is not a current code, only a history code. I got overzealous and erased it before I could view freeze frame data. Oh well, live and learn, I will check on it the next time we visit. I'm hoping it was just a transient fault that won't show it's ugly head again. If it does I'll be hunting down a PCM.
Keith