Unfortunate new panic braking behavior from TACC

[rwiegand]

I haven't done much highway driving for a while, so I don't know when this behavior appeared, but a trip this weekend was made pretty unpleasant by new panic braking behavior. I've always gotten along well with the TACC implementation, but now I'm leery of turning it on and my wife is ready to say we should take a different car on our next trip.

The problem was very consistent on this trip. Five of six times it happened when a car was exiting to the right in front of me. The cars were typically 10-15 car lengths ahead, had gotten fully into the exit lane and my car applied a full panic stop for no obvious reason. Really weird because the road directly ahead was completely clear, and even if it thought the exiting car was in my way there was plenty of room to slow to a stop just with normal deceleration, no braking applied. Of course there were probably 100 times when cars exited in front of me without any reaction from my car. It may be the case that the lane markings were faded in the cases when the braking happened, but I've driven that same stretch of road (Wilbur Cross/Merrit Parkway in CT) dozens of times before.

The sixth incident was even scarier, a car was entering the highway on my right, I was already past it and it was starting to merge into the travel lane behind me when my car decided there was a problem, sounded all the warning gongs, and hit the brakes hard, coming within a whisker of causing the guy merging in behind me to hit me from behind. He was very justifiably peeved with me! Stupidest possible thing to do in that situation.

I've never had a problem anything like this in two years of driving the car. Never seen the so-called phantom braking. I can't remember ever having it do hard braking while TACC was engaged for any reason. Then six emergency hard stops in a couple hundred mile trip. (after the second one I kept my foot over the accelerator ready to override it, but I still got "that look" from DW each time it happened

Is anyone else seeing anything like this? Might it be a problem specific to my car vs a software "upgrade"? The consistency of the response suggests to me a newly introduced flaw in the algorithm.

Currently on v12 (2024.20.7) software.

 

[zwjt3]

TACC has always done this on my 2020 M3 since they turned off the radar. The car seems to always believe that the car in the right lane is actually directly in front of me. Thus any slow traffic in the right lane (or stopped) it seems to treat as an object that is actually in my lane. This is usually most prevalent where the right lane (not my line which is 1 to the left) has an onramp/offramp coming into it. So perhaps the car thinks that the stopped/slow vehicle might merge into my lane. Either way it's pretty terrible and you have to be ready to push the accelerator FAST in case this happens. I learned to simply never use TACC unless I'm in the left lane, or pre-emptively be ready to push the accelerator where the lane to the right of me isn't perfectly straight (I.e., if there is potentially merging traffic in the lane next to me). This helps a lot.

The good news is, that it seems like when using the full-self-drive version I don't have this problem anymore. So it looks like it's improved. It does a much better job of not accidentally deciding the traffic in the right lane is going to come into my lane. I don't think the TACC has been updated in a long time and up until i switched to FSD the auto-pilot was mostly unusable for me unless im in the far left lane.

The next update is supposed to combine the 2 pieces of software (FSD + Autopilot), so maybe all those folks on autopilot might get the benefit of the improved FSD version for highway driving.

 

[rwiegand]

I've used TACC quite a bit and this was completely new behavior on a piece of road I travel fairly often.

The trial period with FSD convinced me pretty quickly that it wasn't anywhere near ready for prime time, so that's a little scary! After one drive using it DW forbade me turning it on while she was in the car because it was so squirrelly.

 

[EVRider-FL]

I don’t use TACC by itself, but I have a lot of experience using FSD, and I don’t ever see this behavior when I drive. Check the Controls > Autopilot > Forward Collision Warning setting and make sure it’s not set to Early or Medium.

Could also be an issue with your cameras. If you’re still under warranty, make a service appointment.

 

[PianoAl]

my car applied a full panic stop

You say "stop," but I'm guessing you don't mean the speed went to zero, correct?

 

[JulienW]

Full panic stop=Fully antilock brakes applied/same as pushing pedal to floor, Large Red Steering Wheel, Loud Beeping, Hazard Flashers come on and car comes to a full stop.

 

[rwiegand]

No it wasn't that. It was hard enough braking to throw us forward into our seat belts and spill her drink in the cup holder. Significantly harder than I've ever had to brake the vehicle while driving manually. I could override it by accelerating. Speed did not go to zero because I hit the accelerator to avoid stopping in the middle of a busy highway.

 

[Lance From Jax]

I have experienced something similar, but it was with a car merging into my lane from an onramp and a car on my immediate left so I was sandwiched. My car decided it was better to brake a bit hard and get out of there.

 

[zwjt3]

I've used TACC quite a bit and this was completely new behavior on a piece of road I travel fairly often.

The trial period with FSD convinced me pretty quickly that it wasn't anywhere near ready for prime time, so that's a little scary! After one drive using it DW forbade me turning it on while she was in the car because it was so squirrelly.

I also used Autopilot for quite some time without having this issue, and this issue showed up when I go an update coinciding with the disabling of the radars.

The FSD is definitely not ready for prime time that's for sure. But it does avoid this particular panic-braking issue better than the old autopilot without radar does. I would say FSD on the highway is mostly decent though (Better than autopilot is in its current state).

I think the old autopilot (when it still had radar) worked pretty well and I used it a lot. Then when I got the no radar update I started having the issues exactly like you are having, and I had to stop using it. Once I switched to FSD it runs well on the highway, but poorly on the local streets.