update July 27:
The dealer agreed that the car was dangerous to drive and requested to keep it another day to run additional tests. Turns out that meant driving it home with a diagnostic computer attached to see if they could replicate the problem. They were unable to replicate the issue. They cleared the 2 errors again, did a recalibration on the body controller and another recalibration on the parking brake controller and asked us to monitor it. I just love how they want me to put my family at risk to see if the problem comes back.
I have a separate case opened with GM Corporate... here's where it gets strange... They have pulled all the repair history from the dealer for the vehicle and have determined that the recalibration of the parking brake performed in June doesn't count as a repair, yet somehow the recalibration of the parking brake and body controller performed last week was a repair. So although they actually saw the problem in June and didn't see the problem a month later and both times there were identical error codes that they read (and documented) and cleared, and the corrective action both times was a recalibration... only one counts as a repair. That makes no sense to me, but probably provides some legal or financial protection to GM.
Apparently the June event has a note that says the technician couldn't duplicate. The one this week didn't have that exact wording but was also not replicated by the tech. It was very difficulty to get a straight answer from the GM Support person why one was a repair and one wasn't - there is clearly some training on how to handle this sort of situation related to consumer safety. Multiple times she referred me to an external site to see the specifics of the California buy back law when I was trying to ask why one recalibration was considered a repair and one wasn't. In my view they attempted to fix the same problem twice and both times couldn't tell me what happened - I think all she was trying to do was get me off the phone.
Coming from an engineering background and working in the tech field for 30 years, I would expect a recalibration to be needed when something has worn, stretched or become corrupt in memory. Think of a position sensor to activate the parking brake on and off. It's binary (on/off) but it needs to know which way to go or how far to pull a cable or push fluid to activate the brake. After a year or normal driving the system suddenly needs a recalibration tells me something has changed somewhere in the system. Yet nothing is apparently worn, everything passes the visual inspection and GM won't authorize replacement of anything that doesn't have an error code and can be replicated by the tech. At this point the dealer is basically hoping it doesn't activate again as their hands are tied by GM on what they can do. By the way, there is a tech bulletin on this, so apparently it's been seen multiple times before - at least enough times to send a notice out to the dealerships. The tech bulletin says to inspect and replace 4 parts for wear and perform the recalibration. Unfortunately I wasn't given a copy, but the parts were brake pads, brake fluid, an actuator and I don't remember what the last one was.
So I will see where this goes next week. I have asked for a root cause, but I don't think they will (or can) tell me why the parking brake activated 2 times while the car was in motion (at low speed) and why it wouldn't release once it self activated, leaving the car in the middle of an intersection one time and in the middle of the road twice. The only similarity between the situations was the car had been recently parked with the parking brake activated and the parking brake self-activated after the car came to a stop and started moving again.