Abrupt Phantom Breaking at high speed - scary

[SkinnyCarGuy]

I recently purchased a 2022 Model 3 Performance that had about 10,000 miles on it and had been owned by two previous owners. I had been enjoying the car until the other night, when I experienced a braking incident while driving at 80 mph on the highway using FSD (latest update).

Scene:
- Nighttime on a dark highway
- I don't remember seeing an overpass

I was using FSD, relaxing and watching the road, when suddenly the car slammed on the brakes. The speed dropped to 40 mph before I disengaged the FSD and sped back up. My passengers were horrified, and if there had been a car behind us, we would have been in serious trouble.

Why did this happen, and how can I prevent this in the future?

 

[E90alex]

Why did this happen, and how can I prevent this in the future?

If we knew why it happened then Tesla would have fixed it by now.

Only way to prevent it is to not use Autopilot or FSD.

 

[stopcrazypp]

I only have experience with AP, but there's a few things you can diagnose:

Did the set speed change? If so, it may be a mapping error where it thought you were on a local road. If so, have you had issues with the GPS popping you onto the wrong road in the map?

It can also do that in certain road junctions, usually before or after a curve. In those cases, the set speed will also drop.

There are other cases where it does not drop the set speed. In those cases, sometimes it is in response to colored lights it feels are either traffic lights or emergency vehicles. Are there any colored lights in the area? If it is because it detected an emergency vehicle, it will show that on the display.

It also seems to be more prone to phantom braking when there is no traffic. I presume you had no lead car and traffic was very light? Sometimes it is in response to mirages or when there is a blind section of the road (either a curve or cresting a hill).

This haven't been proven, but there is a suggestion it only brakes that hard when it detects there is no vehicle behind, which may explain it tends to do so for people when they there is little or no traffic.

 

[SkinnyCarGuy]

I only have experience with AP, but there's a few things you can diagnose:

Did the set speed change? If so, it may be a mapping error where it thought you were on a local road. If so, have you had issues with the GPS popping you only the wrong road in the map?

It can also do that in certain road junctions, usually before or after a curve. In those cases, the set speed will also drop.

There are other cases where it does not drop the set speed. In those cases, sometimes it is in response to colored lights it feels are either traffic lights or emergency vehicles. Are there any colored lights in the area? If it is because it detected an emergency vehicle, it will show that on the display.

It also seems to be more prone to phantom braking when there is no traffic. I presume you had no lead car and traffic was very light? Sometimes it is in response to mirages or when there is a blind section of the road (either a curve or cresting a hill).

This haven't been proven, but there is a suggestion it only brakes that hard when it detects there is no vehicle behind, which may explain it tends to do so for people when they there is little or no traffic.

The highway sign reads "Minimum Speed 40," so it's possible that this influenced the car's behavior. However, it has happened many times before, and the car usually slows down gradually rather than slamming on the brakes. This time, it slammed on the brakes.

 

[SkinnyCarGuy]

I only have experience with AP, but there's a few things you can diagnose:

Did the set speed change? If so, it may be a mapping error where it thought you were on a local road. If so, have you had issues with the GPS popping you only the wrong road in the map?

It can also do that in certain road junctions, usually before or after a curve. In those cases, the set speed will also drop.

There are other cases where it does not drop the set speed. In those cases, sometimes it is in response to colored lights it feels are either traffic lights or emergency vehicles. Are there any colored lights in the area? If it is because it detected an emergency vehicle, it will show that on the display.

It also seems to be more prone to phantom braking when there is no traffic. I presume you had no lead car and traffic was very light? Sometimes it is in response to mirages or when there is a blind section of the road (either a curve or cresting a hill).

This haven't been proven, but there is a suggestion it only brakes that hard when it detects there is no vehicle behind, which may explain it tends to do so for people when they there is little or no traffic.

I was the only vehicle on the road at the time.

Does night driving exacerbate this issue?

If there had been cars behind me, would I have been in danger, or would the Tesla have adjusted accordingly?

 

[stopcrazypp]

The highway sign reads "Minimum Speed 40," so it's possible that this influenced the car's behavior. However, it has happened many times before, and the car usually slows down gradually rather than slamming on the brakes. This time, it slammed on the brakes.

That would explain it. Incorrect speed sign detection may cause it, especially in FSD where there is a city driving mode (different from AP which is expected to be driven at higher speeds).

 

[SkinnyCarGuy]

That would explain it. Incorrect speed sign detection may cause it, especially in FSD where there is a city driving mode (different from AP which is expected to be driven at higher speeds).

It saw the same sign before and gradually slowed down. Why did it slam on the brakes this time?

 

[stopcrazypp]

It saw the same sign before and gradually slowed down. Why did it slam on the brakes this time?

Was there more traffic in the other times or lead vehicle(s)? As mentioned, this tends to happen when there is little or no traffic.

 

[karkrazy]

My phantom braking episodes usually happen during sunset, where I can expect the sun angles and light affecting the cameras. Pure speculation on my part.

And yes, usually no traffic around me.

 

[SkinnyCarGuy]

Was there more traffic in the other times or lead vehicle(s)? As mentioned, this tends to happen when there is little or no traffic.

Likely yes, very interesting. Thank you so much for your help and information.

 

[fholbert]

I recently purchased a 2022 Model 3 Performance that had about 10,000 miles on it and had been owned by two previous owners. I had been enjoying the car until the other night, when I experienced a braking incident while driving at 80 mph on the highway using FSD (latest update).

Scene:
- Nighttime on a dark highway
- I don't remember seeing an overpass

I was using FSD, relaxing and watching the road, when suddenly the car slammed on the brakes. The speed dropped to 40 mph before I disengaged the FSD and sped back up. My passengers were horrified, and if there had been a car behind us, we would have been in serious trouble.

Why did this happen, and how can I prevent this in the future?

It's called FSD Supervised, you should drive watching the road, hand of the steering wheel and a foot ready to press the brake or accelerator at all times. The fact that you went from 80 MPH to 40 MPH without taking corrective action speaks volumes, you're the driver. No need to turn off auto pilot, just press on the accelerator, you might loose 4 or 5 MPH max. It's really not fair to others on the road that you didn't take corrective action immediately.

Besides the items listed above, sometimes this is caused by missing or poorly marked traffic lanes.

 

[gsmith123]

Haven't had a major phantom braking event in years, but if you look back through the old posts around here phantom braking has been a huge complaint over the years (probably most in the 2017 - 2020 era).

Anyway, I don't have any suggestions but welcome to the club.

 

[airpor41]

No need to turn off auto pilot, just press on the accelerator, you might loose 4 or 5 MPH max.

Exactly. I don't see "phantom braking" very often but never lose even 5 mph. You are responsible for controlling your car.

Phantom braking is bad enough. Phantom breaking is truly horrible. I would sell any car that broke like that.

 

[fholbert]

Exactly. I don't see "phantom braking" very often but never lose even 5 mph. You are responsible for controlling your car.

Phantom braking is bad enough. Phantom breaking is truly horrible. I would sell any car that broke like that.

I really think most Phantom Breaking isn’t what it appears and it can be explained.

 

[PCMc]

he highway sign reads "Minimum Speed 40," so it's possible that this influenced the car's behavior.

I've had lots of issues where FSD will misinterpret certain types of signs as speed limit signs.

The 40 mph minimum speed signs that Georgia has posted all along I-75 get interpreted consistently as being the speed limit as 40 mph. I recently did a trip from Indiana to Sarasota, FL, and FSD reacted to every one of those 40 mph minimum speed signs in GA drop the set speed to 40. I learned to anticipate it so the minute I was one coming I'd have my finger on the scroll wheel ready to reset the set speed.

So this is less what I'd call phantom braking and more a case of incorrect speed limit determination.

I have the same issue in Indiana where the signs for state highways are a rectangular white sign with the highway number on it. So IN-135 ends up getting interpreted as 35 mph speed limit and IN-46 many times gets interpreted as 45 mph speed limit. This seems to be an issue with Tesla Vision sign recognition algorithm. I never had this issue with the MobleEye system used for AP1.

 

[fhteagle]

Only way to prevent it is to not use Autopilot or FSD.

Nor TACC. Tesla will absolutely do phantom braking without auto steer being on......

 

[dcfas]

Ten thousand pages posted on phantom braking. I felt the same way the first time I experienced it. My car braked on the highway as I approached an overpass. It was an unnerving moment.

I can say the car takes some time to fully adapt to its, er… quirks. I can imagine certain people probably should not buy a Tesla, as it can be, frankly, dangerous for them. After a year I can finally say I feel safe driving it, but I worry about my wife taking it. She won’t use the cruise or AP at all.

 

[EVNow]

Nor TACC. Tesla will absolutely do phantom braking without auto steer being on......

I thought it will anyway brake because of emergency collision avoidance ?

 

[E90alex]

I thought it will anyway brake because of emergency collision avoidance ?

AEB is a different system than Autopilot. I haven’t really heard of phantom AEB happening.

 

[CyberGus]

This should keep you from being rear-ended