Car suddenly brakes in Autopilot

Car suddenly brakes in Autopilot

I have had a few instances when the car suddenly brakes when in autopilot. I will be cruising around 70 MPH and it suddenly brakes to about 50 MPH without any obstacle or car in the front. Does this happen with anyone else? It is pretty dangerous and I am lucky not to be rear-ended.

82bert | 1 October, 2019

Are you in a construction zone or area where maps are off because of construction? I’ve only had it do this to me in a construction laden area where maps get wonky because of the changes. I learned my lesson quickly.

Effopec | 1 October, 2019

I think the frequency of phantom braking is much higher now with V10. I only witnessed it a few times previously, but I've seen it a lot the last few days. Now I have also been using EAP more lately. My commute is on 40mph surface streets and I never liked the slow acceleration from a start before. That has improved greatly (though there is still too much lag from the time the car in front starts moving before it does), so I've been using it a lot more.

ameetm3 | 1 October, 2019

@82bert - No, not a construction zone. I never use Autopilot in those areas. It was a normal freeway.

ChargedUp | 1 October, 2019

No, but it did once on a regular street at 40 mph, braking and slowing to 25 :(
Luckily not rear ended :)

82bert | 1 October, 2019

@effopec. I’ve had zero phantom braking since v10. Odd you’re having the opposite experience.

cmh95628 | 1 October, 2019

When this happens, I encourage you to file a bug report. Hit the right thumb-wheel button and say "bug report, phantom breaking". Sometime I accidentally report Santa Breaking... ;-)

OC.M3 | 1 October, 2019

Phantom breaking? Shocking. I think sometimes it sees a shadow (maybe a bridge overhead or something) and thinks it's an object in front of you.

majassow | 1 October, 2019

As Halloween approaches, expect to experience more reports of phantom braking....

ameetm3 | 1 October, 2019

@OC.M3 - come to think of it, I believe this has always happened near overhead bridges.. interesting.

howard | 1 October, 2019

82bert | October 1, 2019
@effopec. I’ve had zero phantom braking since v10. Odd you’re having the opposite experience.

NOT REALLY! Everyones drive is different.

lbowroom | 1 October, 2019

I've experienced this as well. However, I think the "sudden" part, the "dangerous" part, and that "we're lucky not to get rear ended" part is grossly exaggerated.

howard | 1 October, 2019

NOT REALLY! Everyone's expectation of safety is different.

82bert | 1 October, 2019


Just wanted to join in on the fun and excitement.

howard | 1 October, 2019

How could you not resist?

M3phan | 1 October, 2019

No spooky brakes for me. None for many months.

Switchmon | 1 October, 2019

I've noticed that there are certain areas where AP will brake even though it's free and clear. I've gotten to know them and plan around them - it's consistent. For areas that I am not familiar with, it is a little disheartening at times, but that's why you're told to keep your hands on the wheel and be alert even if AP is active. I find myself accelerating manually at times to avoid just such issues that may be encountered by unexpected braking, like being rear ended.

garretn | 1 October, 2019

@Switchmon - you're not alone this latest set of releases has made AP very hard to enjoy. I have another thread going explaining my experience with v10.

AP seems more confused now.

FISHEV | 1 October, 2019

Random braking continues to be a problem for the Model 3. You can’t even predict when it’s going to slam on the brakes (or release the Kraken...err....regen). It will see traffic safely in their lanes as a threat and hit the brakes. It will see people in merge lanes 100 yards to your direct right without right of way but the Model 3 buzzing along in the right lane at 75 mph will BRAKE. The oddest one is when passing, clear lane on left, in cruise, turn signal pull out and the Tesla brakes, slightly but incorrectly for no good reason.

But look in the bright side, AP might be a hot mess but we have MORE GAMES!!!

82bert | 1 October, 2019

I could not disagree more with both of you.

FISHEV | 1 October, 2019

We don’t have more games?

mps331 | 1 October, 2019

I have had this experience on a new bridge, where the speed limit below was 45 and the speed limit on the freeway was 65... I also happens during merging...

lbowroom | 1 October, 2019

So no one has been rear ended during this “rapid“ braking? How does someone’s expectation translate this into dangerous?

tahirali98 | 1 October, 2019

this happens to me almost every time I use autopilot. Sometimes with cars next to me, sometimes with an overhead object (bridge, toll reader, etc), sometimes in wide open space. All I can say is be careful drinking coffee while on autopilot.

lbowroom | 1 October, 2019

Ok, spilling coffee can be dangerous

RES IPSA | 1 October, 2019

I have not had phantom braking for a while, but I have had more cancelled lane changes recently for not apparent reason.

tdwin2000 | 1 October, 2019

I noticed of course that in version 10 the car accelerates from a dead stop while in Autopilot more rapidly. However, I also noticed that the car is very slow to start moving when a car in front of mine suddenly turns out of my lane. I haven't noticed sudden braking like the OP posted but I have noticed on highway I595 her in Ft Lauderdale area that there is a certain stretch of highway where my auto lane change will not work. In fact I was apparently approaching this area this morning and pushed my turn signal down to auto lane change. IT started to change and then shot my car back into the lane I had already been driving in. I couldn't help but think there is something in this area that is not allowing the car to auto lane change and how dangerous it could have been if there was another car in the lane when it shot me back from the lane where I started.

FISHEV | 1 October, 2019

"So no one has been rear ended during this “rapid“ braking? How does someone’s expectation translate this into dangerous?"lbowroom

That's what the Russian Roulette players said until....

Random, unnecessary braking is inherently dangerous. Speed increases the danger.

-TheJohn- | 1 October, 2019

Weirdly it's super rare for it to happen to me in Tucson and surrounding areas but on a recent trip to the Bay Area I finally ran into it a fair amount. Even encountered the phantom overpass problem finally.

To switch subjects.. The thing that drives me crazy is when the car refuses to allow you to go more than 5 mph above the limit when said limit is at 65. 90% of the time it'll let me do any dang thing I want to in terms of speed at that speed but sometimes it gets cranky and auto shifts it back to 70.

lbowroom | 1 October, 2019

Russian roulette 1 in 6. Rear ending 0 in 1,000,000? Yeah, pretty much the same

howard | 1 October, 2019

lbowroom | October 1, 2019
So no one has been rear ended during this “rapid“ braking? How does someone’s expectation translate this into dangerous?

Just curious what reference you have for no one has been rear-ended during "rapid" breaking? That is a near comical statement.

Any unintended breaking in heavy fast moving bumper to bumper can result in a rear-end collision. It seems like most accidents you see are rear-enders. With all the incredible distracted drivers these days why in the world would you want to add any element of additional risk whatsoever? It is why I don't use any of the advanced driving features. Don't intend on it unless they are no longer beta and/or it is a very open 4 lane road.

priit | 1 October, 2019

I have noticed phantom breaking on autopilot if there is nothing on the side of the road for a while and then when the car notices a parked vehicle or a bush or any other object on the side of the road. It slows my speed by about a third like being scared that the object might jump in front of the car suddenly, then it appears to make up its mind, that it is dealing with something that is stationary and speeds back up to normal speed. This appears to happen also sometimes with higher sidewalk or sometimes even a rock beside the road. It would appear that the car does not detect those things far enough ahead or make the decision about them when they are far enough ahead that it would not need to change speed. I hope the autopilot AI will learn to recognize those from further away, so it would not need to do so sudden unwarranted breaking on an empty road.

82bert | 1 October, 2019

@priit. Never have this happen. Even with cars parked on the side of the road.

Hal Fisher | 2 October, 2019

I noticed since v10 that the car moves around in the lane more. Watching the screen it continually thinks another car is more in my lane than it is (a car was not in my lane but maybe a bit closer). When a car is close behind and others all around I’ll sometimes just put it in manual driving so I don’t have to worry about anything going wrong. I’d bet musk has started tinkering with the algorithms and finding that it’s not that easy to guesstimate distance with single low cameras on the side.

Hal Fisher | 2 October, 2019

Doesn’t anyone think it’s odd musk listens to twitter and other bs news more than his own forums? Guess he doesn’t want to read the truth.
Also, dancing cars when stopped REALLY shows how poorly it can determine object movement.

M3phan | 2 October, 2019

The dancing cars has completely stopped for me in V10...

calvin940 | 2 October, 2019

@M3phan | October 2, 2019
The dancing cars has completely stopped for me in V10...
Haven't seen them yet in V10 for me either nor do I believe the visual representation of the cars are an indicator of the back end recognition system.

T-Dog | 2 October, 2019

Happened to me on v9 software in slightly congested freeway traffic at night while taking a bend. I was thinking it must have thought my M3 in AP calculated that it was going to run into the car in the in the next lane also taking the slight curve. Quickly took it off AP and drove the rest of the way.

Remembered auto steering is still in beta so I’ll probably stay away from it until beta testing is done.

teslamazing | 2 October, 2019

Would u rather have the car brake or possibly hit something it is seeing/not seeing

There is no denying some ppl r experiencing phantom braking. How many incidents are there where a car was rear ended as a result? Hmmmm...


teslamazing | 2 October, 2019

Also @ameet did the car get back up to 70 mph or stayed at 50 mph? Speed limit bug ? I had that happen where the car went from 65 mph to 50 then back up to 65 because the car thought the speed limit
was 50 for a minute but in reality it was not.

lbowroom | 2 October, 2019

“Just curious what reference you have for no one has been rear-ended during "rapid" breaking”

This forum and my news feed, where’s the thread or article about the car that got rear ended due to phantom braking?

“fast moving bumper to bumper”

What does that even mean?

82bert | 2 October, 2019

I use NoA and AP roughly 50 miles most days with a lot of interstate use and still zero phantom braking, no erratic behavior while centered in lane, and no dancing cars SINCE V10. The only issue I’m still having is that there are a couple on ramps that, if I’m in the far right lane, it wants to go to the right with the widened lane then quick correct as it narrows back to a normal lane. This doesn’t happen along every on ramp. I’m confident it will be fixed with time as well. Some of these other comments about AP on V10 being worse sound insane to me. I’ve never seen it this good.

Also, I’ve yet to see a dancing car since V10. Maybe a tiny shift or a further away car disappears then comes back, but no spinning/dancing.

82bert | 2 October, 2019

@lbowroom. Agreed. Also, phantom braking that I’ve had in the past and heard about is at faster speeds when there should be more room between cars. Definitely never had it at “bumper to bumper speeds”. And there’s no such thing as “fast bumper to bumper”. That’s just asshole driving with tailgating, and not legal.

stephenfootball | 2 October, 2019

Phantom braking seems much better for me with V10. :)

Joshan | 2 October, 2019

When I get people to actually talk about their "phantom braking" experiences it is rarely phantom and usually the same issue.

Anytime you have phantom braking look at your speed, did the max speed suddenly drop? Seems to be more map issues and it thinking you are either not on a highway or the speed is incorrect for a short time.

82bert | 2 October, 2019

@joshan. This is exactly what I was referring to earlier. That being said there is real phantom braking that seems to be activated by bridges/shadows, but so far not on V10 for me.

teslamazing | 2 October, 2019

@joshan exactly.

lbowroom | 2 October, 2019

“ dancing cars when stopped REALLY shows how poorly it can determine object movement”

Uh, no. If anything, it’s an indication that the algorithm is tuned to detect the smallest increment of motion. It’s works when things are moving, not when they are static. can’t really get hit by something that’s not moving.

cmh95628 | 2 October, 2019

@joshan. re: phantom breaking caused by mis-mapped speed limit. Interesting thought. I will have to keep an eye out for this if I ever get phantom breaking again. Thanks for sharing.

M3LR2018 | 4 October, 2019

Happens frequently on freeway with nothing in front for well over 500 yards.

derotam | 4 October, 2019

70 MPH and it suddenly brakes to about 50 MPH

- Why are you letting it decelerate 20 MPH!!! I have had phantom braking and I never let it drop more than probably 5mph

howard | October 1, 2019
heavy fast moving bumper to bumper

Huh? I can see heavy bumper to bumper traffic. but usually not much high speed is involved when you say "bumper to bumper" unless you are talking NASCAR, but I don't think they have a phantom braking issue.