Flesh2112

Looking for opinions on an odd, but somewhat scary incident with my 992 that happened two nights ago.
In summary- temporary brake failure at low speed in stop and go traffic and I hit a tractor trailer in front of me.
Personal and Car History-
2020 911 2 S Cabriolet. Purchased new in February 2020.
30 years of driving - not a single accident, and only 1 ticket.
Due to Covid, the 911 has been an occasional driver and at the time of the minor accident it had 2800 miles on it.
No mods and (was) in mint shape.
I Took a trip to the beach for Halloween and put 975 of these miles on it then. On way back to TN, through GA and the NC mountains, the car drove perfectly and was a dream. My wife and I bragged on it several times.
We stopped after about 6 1/2 hours of driving (two gas stops) to eat before what would have been the last 40 mins home. On I-40 there was a major accident, so we were in stop and go bumper to bumper traffic for 50 minutes. Atlanta and LA kind of traffic
The Car settings at time of brake issue:
Normal mode with auto start and stop enabled, PDK in manual mode (to avoid the jerky shift of stope and go 5 mph traffic).
After I would guess close to 100 stop and starts in that time sitting in traffic, I went top slow from about 10 mph as the Semi in front of me slowed and
the brakes just didn't work. I could tell they were not working immediately and said to my wife- "I can't stop" and she said after it all that "I was standing on the brakes." The car continued for about 10 feet and hit the black bar the was on the back of the semi trailer (to avoid people like me going under the truck). I would guess I hit this at about 6 mph. The car went into auto STOP mode. And after a moment of disbelief, the truck in front moved forward (did not notice I hit him) and the 911 auto started and everything worked fine. I got out to flag down the Truck driver but he just said, "I didn't feel anything" and he looked at his truck- saw no damage and he went on.
Under my foot the brake pedal felt firm, about halfway down and didn't budge or move. No ABS sensation. The road was dry, it outside temp was 60 degrees and the car had only been on for about 1:15 before tis occurred, in stop and go conditions.
My wife and I can not remember if the auto stop occurred as we slowed or just as we hit the truck.
For sure I did not hit the accelerator, the floor matt was NOT on the accelerator and It was not user error.
We sat in traffic another 10 min until we cleared the wreck and the car was fine on the intestate and back road trip home (another 30 min after) I switched to automatic on the PDK and it drove home fine- albeit cautiously on my part.
Damage was a dent across the bumper and some paint damage (MINOR for sure).
I took it to my Porsche dealer yesterday and gave them the facts and the time of day it happened. They said- "Everything is fine we can't reproduce the issue."
Cost of repair $2000. The car is still at the dealer so I can't post pics.
So any thoughts?
I feel it was a confusion in the electronics do to the Auto start stop. Also many times in that slow stop and go, the "Parking view" often came on the main info screen and maybe it was tricked into some kind of parking mode and did not detect the bar across the back of the semi?
I had been using ACC on the trip but was off at those speeds. The car is highly optioned and has PASM and all the modern electronics.
Anyway, I am going to talk with Porsche North America about it but since the dealer says all is well, I doubt they will care much at a higher level.
I am going to pay for the fix out of pocket, but my big issue is how do I avoid this in the future. I can envision rolling into a busy intersection if this happens again and getting nailed by cross traffic.
At least I know (painfully) know where the electronic parking brake it must in case.

RF

RD16RR

Sorry to hear it...even better nobody hurt - at least it was a slow speed bumper tap with minimal damage - the fact the shop couldn’t reproduce it is always frustrating - keep the forum updated

Flesh2112

No resolution from Porsche. Most likely was parking assist and the auto on / off caused a glitch that had the car in a strange state of paralysis.
damage was $2000 for bumper repair, Paint, a few sensor replacements and laser sensor alignment. But all in all not bad. Local Porsche dealer treated me well but just couldn’t reproduce it so won’t cover it. I don’t have the time or energy to turn Karen and go up the ladder, so live and learn and was su j a small thing it’s not anything that would devalue the car.
Now I only drive in sport and sport plus and wet when needed. I could just dig in the menus and disable auto stop but sucks to do that each time I get in.
RF

Tupper

^ Wow. Another reason why Auto Stop/start is so annoying (and dangerous).

I'm just going to drive in Sport mode from now on.

Denny Swift

Wow that’s a strange one. Glad you’re ok. I can’t imagine how it could be related to A.S.S. That doesn’t make any sense. The brakes are hydraulic and A.S.S. does not affect the brakes in any way. There is an electric brake booster in the 992, but it’s still a hydraulic system. Stepping on the brake pedal presses the piston into the master cylinder and that creates hydraulic pressure that clamps the pads onto the disks. It’s mechanical. As far as I know, there is no electronic system that can defeat that. Even with the engine off, the brakes should work. If you were pressing lightly on the brake and the electric booster malfunctioned, I’d think that could cause the sensation of not having brakes, but you say you were standing on the pedal. I certainly believe you’d do that in the situation you describe. But if you press as hard as you can, I don’t see how the brakes could fail. This is really a strange one. I’d think that Porsche would at least be able to tell you how a brake failure could occur. I can’t think of any.

gohawks23

User error, most likely hit accelerator and brake at same time.

Tupper

^ You mean he was trying to initiate a launch control in bumper to bumper traffic?

Now THAT takes *****

Flesh2112

Yeah I figured someone would call “user error.”
I asked Porsche to look at the computer for that, just to make sure I wasn’t crazy.
They said the impact was at 6 mph and no acceleration they could see. I’d think hitting the accelerator would have had me lurch faster, as we were basically coasting. And I was standing on the pedal with my right foot, not left- I’m not a two footer.
That is the simple way to explain it but I just don’t think that was the case.
I love the car so I’m taking the risk- except I’m gonna stay away from the auto start/stop.
No issues for 400 miles since.

Luckily my R8 and 458 don’t have it!
RF

Mercuriell

Might be worth developing the mindset that Parking Brake can be used in emergency

Flesh2112

I couldn’t find that little button in the heat of the moment!

Mercuriell

No I wouldn’t be able to either but I thought in the past it might be worth while rehearsing the move!

Denny Swift

I forgot about the computer logging information, but I thought the data was only stored in the event of a “crash.” Evidentiary 6 mph was enough of an event to make the computer record the data. The pressure on the brake pedal should have also been recorded along with the angle of the steering wheel, seat belt use, and a couple of other data points. If you didn’t already ask them, for the data on the brake pedal, you need to. If the data shows that you indeed were standing on the brake pedal, then they need to buy your car back and study it to figure out WTF could possibly explain how that could have happened. Because as Scotty would say, “Dat defies da laws a physics.” Total brake failure is pretty much impossible without the lines blowing out or the master cylinder jamming. And then the problem suddenly fixing itself is also inexplicable.

Also, blaming it on the A.S.S. is a poor excuse. Ask Porsche how that could be possible. It’s not possible.

gohawks23

I agree...ice/slick road?

rk-d

Agree - forensics would be revealing. I would push Porsche to do this (something your dealer would need to advocate, b/c I suspect it's something that PCNA would need to do - probably involving Porsche AG)

Flesh2112

it was October in TN and was 75 degrees and dry. The pedal did not go to the floor was about midway down and not going further- from my memory.
I didn’t ask about brake pressure and such. I’ll do that maybe at some point.
Was just strange that we had been in stop and go traffic for an hour due to a wreck ahead and it was all good and then sudden issue.
Initially I was high on fighting and making Porsche buy it back. But then I just kinda got over it. Maybe I just want there to not be anything wrong. Maybe I’m tired of trying to figure out gremlins with a lot of things.
Or maybe I just live the car that much.