So the OP has been lectured about trusting AP - fine, it had to be said. Some people have said that AP has a well documented affinity for trucks. And Tesla have supposedly said AP behaved as designed ... apparently by drifting or turning into an adjacent lane on a straight road.
For me, a recent purchaser of a CPO with AP, these last two items are of concern. When I take over from AP manually (to change lane) there is a reasonable force needed to get it to 'let go'. The one time it tried to curb me on the median curb, again it was reasonable effort to get it to 'let go' in time (ICEs apparently curb there a lot too - as all the rubber cannot just be from Teslas). Point is, reaction times are not what you'd all like to believe they are, and then there is the need to exert enough force to get control. It seems very plausible to me that a rapid move would create an unavoidable collision - even with your hands on the wheel - which I have all the time.
Question is - what is normal and expected about the vehicle changing lanes on a straight road? Even if it was blinded by the sun (I've seen this a number of times already with only 4 weeks ownership)?
My personal theory, based on very limited experience. OP was driving on AP. At a point prior to the impact AP disengaged as it could not 'see' properly - so the vehicle was actually driving on TACC instead. With no vehicle close enough or locked to follow, the car will drift at that point. And if the OP was "looking straight ahead" - it would be easy to miss that drift.
Behaving as designed could be "disengaged appropriately when it was unable to offer safe assistance".
Reason this is my theory. I had mine go from AP to TACC 'silently' - which is to say I did not hear the disengage noise just yesterday. Happened to notice blue wheel went gray, and speed indicators were blue indicating TACC engaged. I do not drive with music loud, and was not distracted.
AP is definitely not the safety feature I thought it was on purchasing, and with 20:20 hindsight I'd not spec AP1 or AP2 for a current purchase - too many unknowns related to future perforamance.
The assertion this would not happen with fully enabled AP2 is certainly a good thing to hope for - better sensors, and better decision making. But at this point this thread does not offer a definitive cause - so just as I am speculating that AP may not have been engaged, there are a myriad of other reasons it might have happened which may or may not be affected by different hardware.
Best advice in the thread (and elsewhere). It's Driver's Assistance, always have hands on the wheel, always be just as aware as you would be if in direct control - and at that point, it's no more than an emergency alert and possibly a sleep/wander warning/avoidance system. Which makes it a very expensive addition.
The more people I read worried about having to set their AP to the speed limit, and who say they are driving 50-100 miles per day and AP is essential - the more pleased I am that my commute is 4 miles each way, and my primary MS driver does little highway. It's not a novelty or toy, but it's also not what many people are treating it as - and it certainly has proven in short order it's not the safety feature I was hoping it would be for the driver I purchased it for!
