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Question about ACC and "Phantom Braking"

joec

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One of the most critical issues I have with Tesla is their refusal to properly address "phantom braking" when using either Autopilot or FSD.

To anyone unfamiliar, phantom braking is when you have your cruising speed set to, say, 75 mph, and you're on an open stretch of highway with no other cars in front of you, and the car suddenly and harshly brakes down to about 45 mph for no reason whatsoever.

There are a lot of theories as to why the car does this. Earlier models, like mine, that still have radar hardware seem to exhibit the problem more than others, even though the latest software versions are supposed to be ignoring the radar data. And it seems to happen on 1-lane roads more often than multi-lane highways. Particularly if there's a small road intersecting that 1-lane road, or passing under it. (One theory is that the GPS is mistakingly placing you on that smaller intersecting road, which has a much lower speed limit, and the car thinks you are suddenly speeding by 35-40 mph. Still no excuse for slamming the brakes, but whatever.)

In any case, Tesla has known about this for years and has made no attempt to address it, as far as I can tell.

It basically renders all forms of Adaptive Cruise Control useless on the car for me, as I have no interest in being rear-ended when my car suddenly slows down that hard for no reason. It also scares the crap out of my passengers. So I've had to suffer through longer road trips holding my accelerator pedal down manually. Like an animal.

My question: Has anyone experienced anything remotely like this on the Lucid using ACC? I've driven other cars with ACC from Audi, BMW, etc. and I've never had an issue. Slowdowns, when they happen, seem to happen for the correct reason. (The car in front of me slowed down.)

I'd love to know if anyone here is having this issue with their Lucid. Because of all the issues I've been hearing about here, that would maybe be my only dealbreaker.
 
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milgauss

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No issues of phantom breaking after about 900 miles on ACC. My only issue is the aggressive regen braking when you disable ACC, but that can be easily fixed in SW or you learn to compensate with the accelerator before disabling (not ideal). Overall, I think the ACC on the Lucid works better than my previous Teslas.
 

HC_79

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No issues for me after about 1200 miles. I agree with @milgauss about the aggressive regen braking but I also just override the ACC by putting my foot on the accelerator and then disengage it via the steering wheel.

I also like how you get the option to change the speed when a new speed limit is detected vs the car just doing it automatically. On my previous Audi I had to turn it off as every now and then it would read the truck speed limits on the freeway and then just slam the brakes on to drop to 55mph. With the Lucid is flashes that the speed has changed and you can tap the button to adjust or just ignore it.
 

hydbob

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Same here 5200 miles, about 4000 when ACC was available, not a single instance of phantom braking. I also have my ACC set to follow distance 3 instead of the animals on here who have it set to 1. 🤣
 

joec

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Thanks for all the responses so far. Puts my mind a little more at ease. I assumed it was a Tesla-specific issue, but I wanted to be sure it wasn't rearing its ugly head in the Lucidverse.

I'll probably get Dream Drive Pro on my Touring, regardless. Just because I'm a tech guy, and I'm fascinated with the concept of self-driving, even if I almost never use it in practice. But all I really want is a good ACC system for those longer drives. Hours 8+ are a killer when you've had your foot holding that accelerator the whole time.
 

borski

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Just to add to the chorus, 5000 mi in and not one instance of phantom braking. Love the ACC.
 

Dortreo

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Is it “breaking” or “braking”? Because ”phantom breaking” seems like it could be a thing.

I wonder if only Teslas have phantom braking because they rely solely on visual sensors so don’t have a redundant means of checking using a different medium. I believe radar is used for ACC in most cars, including Lucid?
 

joec

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Is it “breaking” or “braking”? Because ”phantom breaking” seems like it could be a thing.

I wonder if only Teslas have phantom braking because they rely solely on visual sensors so don’t have a redundant means of checking using a different medium. I believe radar is used for ACC in most cars, including Lucid?
Good catch on my typos. Fixed.

Like I said, many theories out there. But no one has ever really explained it. Including Tesla. One of many reasons I will not be buying another one.
 

Adnillien

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With the Lucid is flashes that the speed has changed and you can tap the button to adjust or just ignore it.
It seems to flash the speed limit has changed message everytime it passes a speed limit sign even when the speed has not changed. Is it trying to tell me that I am driving too fast?:D
 

Whidbey_LucidGT

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It seems to flash the speed limit has changed message everytime it passes a speed limit sign even when the speed has not changed. Is it trying to tell me that I am driving too fast?:D
I know, that is silly & they ought to fix. Current speed limit 65, you pass a sign "speed limit 65", it re-prompts you.
 

DeaneG

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I wonder if only Teslas have phantom braking because they rely solely on visual sensors so don’t have a redundant means of checking using a different medium. I believe radar is used for ACC in most cars, including Lucid?
My 2018 Model 3 has radar + cameras and does occasionally phantom brake. Elon mentioned that the radar has a low signal to noise ratio and contributed to errors, so they eliminated it.
 

joec

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My 2018 Model 3 has radar + cameras and does occasionally phantom brake. Elon mentioned that the radar has a low signal to noise ratio and contributed to errors, so they eliminated it.
Yeah, that was his explanation, but it doesn't explain why it's still happening to those of us who have the radar. Presumably, they could just disable the radar in software.

And for me, it's a lot more than occasionally. It's all but guaranteed to happen on single-lane highways within 5-10 minutes of engaging. On multi-lane highways, it is less frequent, but it still happens enough where I simply don't trust it.
 

Demosthenes

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So I've had to suffer through longer road trips holding my accelerator pedal down manually. Like an animal.
LOL burst out laughing at this comment hahaha

On a more serious note, I’ve only driven about 1k miles and have only extensively used ACC on one round trip between San Diego and LA, but so far it’s been amazing. Zero phantom braking and the way it handles car cutting in and out in front of me is superb, extremely smooth. I don’t even mind that it needs to be re-engaged after a full stop cuz it’s a simple press of a button. Only two minor quibbles are that after re-engagement it seems to default to 20 mi/h instead of whatever your previous setting was and it can’t be set above 90 mi/h.
 

hydbob

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LOL burst out laughing at this comment hahaha

On a more serious note, I’ve only driven about 1k miles and have only extensively used ACC on one round trip between San Diego and LA, but so far it’s been amazing. Zero phantom braking and the way it handles car cutting in and out in front of me is superb, extremely smooth. I don’t even mind that it needs to be re-engaged after a full stop cuz it’s a simple press of a button. Only two minor quibbles are that after re-engagement it seems to default to 20 mi/h instead of whatever your previous setting was and it can’t be set above 90 mi/h.
lol @ can't be set above 90mi/h
 

Paladin732

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LOL burst out laughing at this comment hahaha

On a more serious note, I’ve only driven about 1k miles and have only extensively used ACC on one round trip between San Diego and LA, but so far it’s been amazing. Zero phantom braking and the way it handles car cutting in and out in front of me is superb, extremely smooth. I don’t even mind that it needs to be re-engaged after a full stop cuz it’s a simple press of a button. Only two minor quibbles are that after re-engagement it seems to default to 20 mi/h instead of whatever your previous setting was and it can’t be set above 90 mi/h.
If you tilt up instead of pressing in the wheel button it will resume at your previous speed.
 

PCorkett

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No issues of phantom breaking after about 900 miles on ACC. My only issue is the aggressive regen braking when you disable ACC, but that can be easily fixed in SW or you learn to compensate with the accelerator before disabling (not ideal). Overall, I think the ACC on the Lucid works better than my previous Teslas.
Completely agree. The SW fix I’d like is when I disengage the ACC it should not apply the regen until I touch brake or lift my foot from accelerator. (Could be an configurable option.)
 

Dortreo

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Just did a 200 mile drive tonight using mostly ACC. A few observations: Lane Keep Assist basically sucks. Even on decent roads, it can’t tell what’s a lane and what isn’t, so the wheel can randomly jerk. On ACC, I used the 2 spacing setting. 1 was getting too exciting with sudden slowdowns in traffic. Otherwise, an excellent experience.
 
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