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Sudden deceleration while on adaptive cruise control only

Sudden deceleration while on adaptive cruise control only

So today when driving home, my model3 suddenly decelerated while cruising at 60mph. There was no significant traffic in front of it that would indicate an eminent collision. Also not present was any audible warning. It slowed from 60 to 30ish. Fortunately there was no car behind that rear ended me. I quickly filed a BugReport using the voice command. I had dashcam on and have recorded the sudden deceleration. It is clear that there was no car merging into my lane.

So I am not sure if this is adaptive cruise control algorithm failing and/or evening lighting conditions (its a city interstate, not some dark highway in country). How does Tesla respond to the specific bug report to validate whether it is a sensor issue or algorithm issue?

How often have people experienced such a sudden deceleration? I drive on the same road everyday, often with AutoPilot/FSD on and works flawlessly, except today. I have the latest released update (Jan 2020).

FISHEV | January 8, 2020

"How often have people experienced such a sudden deceleration? "

Unexplained braking on Model 3 adaptive cruise is long standing problem. Many of the owner posts here about it have been deleted but you'll find it is common topic on all the various Tesla Forums.

The problem is that Tesla's adaptive cruise is hostage to the "Full Self Driving" features so it has been made overly cautious (braking for overpasses, shadows, cars safely in their own lane), seeing threats that don't exist or more correctly seeing situations it cannot interpret correctly so it brakes to be cautious.

Also, the adaptive cruise is hostage to the maps as it will reduce speed if it thinks the speed limit changed.

So outdated maps and inability to correctly interpret surroundings are the cause of the random braking. What makes it worse is that Adaptive Cruise thinks it is just taking off accelerator but regen then kicks in causing a hard brake vs. the car just coasting. Lack of integration between adaptive cruise and regen.

FISHEV | January 8, 2020

This is just the adaptive cruise in AP, not any "Full Self Driving" functions.

jansenhvac | January 8, 2020

Has happened to me twice on the same Hyw 11 at the same stretch from 100 km down to 50 km. I had a look at it afterwards in this particular area a city road runs parallel to the Hyw. On the screen it indicated the 50 k speed limit after about 100 m changing back to 100 km, must be GPS related

Vtpnw | January 8, 2020

This really sucks. I have videos of when this happened from dashcam. Wish there was a way to share it on the forum.

In all these instances, did the car give audible warning as to what it thought was happening? I hear such things when I am at a higher speed than the car likes as I approach the stop light with cars in front. But not in this case. I wonder if the fellow forum members heard any audible tones.

Also, is there any follow up excepted on the bug report filed? I wonder if anything specific happens beyond Tesla collecting this as a AI model training datapoint or something.

cgreen | January 9, 2020

This has happened to me as well. I didnt notice til the latedt jan 2020 update. The car would drop from 70 to 50 or so then back to 70 very jerky action. it seens to do this when at an overpass or on off freeway ramp. im a brand new owner so take what i say with a grain 9f salt. still getting used to it. i do have FSD as well. not sure which mode it was on when this happened.

cgreen | January 9, 2020

happened at the same areas as well at least 2 diff. times.

HighlandPony | January 9, 2020

Yup, this happens. Albeit less frequently than it did on my 2016 Toyota RAV4.

rraoster | January 9, 2020

I had a similar odd episode driving in stop and go traffic in my MS. The car, in FSD, was at a complete standstill, with no one cutting in, when it turned off: went to park, turned on hazard lights and flashed a message saying cruise control off. I reengaged to drive to continue but the steering wheel icon for FSD and the cruise control icon would not light up for the rest of the ride. I finally did a soft reboot to bring things back to normal.

LostInTx | January 9, 2020

I've had this happen on numerous occasions. It's very unnerving because if the guy behind you isn't paying attention, there can be a boom, even if you disable EAP and accelerate within a second or two.

Keep feeding data to Tesla in the form of bug reports and we'll hopefully see fewer of these instances going forward.

SalisburySam | January 10, 2020

Yup, this is the infamous phantom braking that has plagued TACC since its introduction and is a common annoyance in my car. It is also the reason my wife (or any passenger) won’t let me use it with her (them) in the car. I wish I could say it has gotten better but I still experience it on v40.50.7.

Some things to look at: when it happens, quickly glance to the road speed limit the screen is showing. I’ve noticed on at least three occasions a major road over- or underpassing the road I’m on has a different and lower speed limit. The car sees this and brakes. In a few seconds the speed limit returns to the correct one, you try to explain what happened to your passengers, and you check to see if you or they have a laundry problem that needs immediate resolution.

Just let me turn off the TA part of TACC when I want to. Is that so hard?

howard | January 10, 2020

SalisburySam | January 10, 2020
Yup, this is the infamous phantom braking that has plagued TACC since its introduction and is a common annoyance in my car.

It is also the reason my wife (or any passenger) won’t let me use it with her (them) in the car.

I wish I could say it has gotten better but I still experience it on v40.50.7.

Just let me turn off the TA part of TACC when I want to. Is that so hard?

+1

It would not be hard to do just not a priority at all. Has not been the nearly 1 /12 years I have owned the car. Seems every other brand has a great functioning Adaptive Cruise but not my expensive Tesla!!! How will you Ever have any kind of FSD when Tesla cannot fix phantom breaking???

teslamazing | January 10, 2020

All these complaints of sudden deceleration but how many have actually had an accident occur ? Hmmm..

teslamazing | January 10, 2020

People keep saying “fortunate”

Is it really fortunate? Or does the car already know in combination?

WW_spb | January 10, 2020

Poor Howard, maybe sell your 3 and get on the wagon with Fishstick to get MachE?

Kellisday | April 11, 2020

Has happened to me in our S many times and the wife is getting MAD.
Also, when in TACC doing 65 and changing from one freeway to another freeway, it will change my set speed to 80. Not cool!
Does anybody listen or care when you do a "bug report".

David41 | April 11, 2020

I experience the sudden braking. I think it is because the car wants to reduce the speed to what would be safe on an adjacent offramp. This is crazy dangerous (someone is going to get seriously rear-ended) and with all the observations of this behavior I think Tesla is going to be subject to a large Federal penalty, a large indefensible lawsuit, and more really bad publicity. I am surprised they have not yet fixed the issue. I drive a 2020 'S', delivered less than a month ago.

lbowroom | April 11, 2020

Many drivers without any autopilot slow on overpasses for no reason without getting rear ended. That argument had no legs. Also, I don’t understand why anyone would allow the car to slow so much. Do you not realize that you’re right foot has ultimate control over your speed? Do you do so just to prove s as point? It’sa driving aid, not autonomy. OMG, the car is slowing, I have no choice but to ride it out and wait until it speeds up again. Sheesh, push the pedal!

Same goes for the auto-wiper. If it’s taking a little longer to wipe than you like and you can’t see, you don’t have to wait or fumble with switching to manual on the screen, just tap the end of the stalk. Stop being so helpless.

georgehawley.fl.us | April 11, 2020

We have a 2018 M3 that suddenly decelerates when a car next to us in the right hand lane on an interstate heads off to an exit ramp. I don't use TACC on secondary roads any more because of several quirks like that. Tesla recommends against using it on such roads anyway.

They have a lot of work to do to polish autopilot functions let alone FSD. I wouldn't hold my breath.

howard | April 11, 2020

Oh lbowroom having a little tantrum. How cute. Your defense of Tesla is well defenseless. Let me be specific that my 2019 Volt has much better adaptive cruise control. Why is that?

lbowroom | April 11, 2020

Because it’s less capable. It merely tracks the car directly in front of it not considering anything else.

lbowroom | April 11, 2020

The car isn’t FSD yet. If you can’t catch the speed dip within 5mph I suggest you not use it.

lbowroom | April 11, 2020

How is that logic defenseless? It’s extremely easy to understand.

lbowroom | April 11, 2020

I can draw you a flow diagram, would that help?

lbowroom | April 11, 2020

Do you still believe that every sales location has specially programmed cars that trick you into buying the car?

howard | April 11, 2020

lbowroom, OP said adaptive cruise only. That is what we are comparing. I drive both back to back. The Volt is substantially better. I don’t need to hover my foot over the throttle trying to anticipate a rapid deceleration because my Tesla can’t track the car in front of it properly. No diagram needed or further explanation really. I have no idea about all the others sales locations but the Cherry Creek location demo was just amazing. So amazing I have never been able to repeat it. Perhaps the demo models had driven the same route a few thousand times that it learned on its own. You know like the infamous FSD demo videos produced by Tesla. Proof it can be done on a specific choreographed route. Sorry your feelings are hurt again.

lbowroom | April 11, 2020

You didn’t insult me, nor did you best me. Why do you imply that my feelings are hurt? Do you think that calling me cute belittles me? Like raqball with his tireless links to kiddie clowns? I recognize language that’s designed to make people cringe. You’re a good manipulator.

howard | April 11, 2020

lbowroom, The demeanor in your five posts in a row felt like I had slighted you in some way. My apologies either way.

lbowroom | April 11, 2020

No need to hover your foot over the pedal, plenty of time to get it up if you lose steam.

fazman | April 11, 2020

@howard, you seem like a normal person on this forums. I like the way you communicate ideas. most others with multiple posts back to back... i find suspect.

WW_spb | April 12, 2020

Volt is soooo great that GM discounted it. Lol bye bye Howard.

FISHEV | April 12, 2020

howard | April 11, 2020 So amazing I have never been able to repeat it. Perhaps the demo models had driven the same route a few thousand times that it learned on its own."

I think it may have to do with time of day and lighting. I get a lot of braking for overpasses and I've noticed that when the light is directly behind me and makes the overpass brighter there is more likilhood it mistakes it for a turning tractor trailer.

So you may try to replicate it but it doesn't work because...https://youtu.be/G5zPqgQ67yo?t=30

teslamazing | April 12, 2020

AP is phenomenal. Lots of improvements with NOA. Unsure why ppl talk so down on it, esp the ones that say they haven't been using it for a very long time in lieu with knowing so much about it..

teslamazing | April 12, 2020

Also lots of " Fortunately there was no car behind that rear ended me"

Been saying this for months, its it really fortunate? You don't think the Tesla would react differently IF there was a car behind you?
Can of you provide examples where the sudden breaking actually was the root cause of an accident?

Back to sippin my tea.

teslamazing | April 12, 2020

its it = is it *

HighlandPony | April 12, 2020

Comparing TACC on my M3 to the adaptive cruise control on my RAV4 in terms of unexpected deceleration I’d say they are comparable. Both cars do this from time to time. I’d say Tesla is on par with Toyota, no better no worse. My 2 cents.

teslamazing | April 12, 2020

"I’d say Tesla is on par with Toyota, no better no worse. My 2 cents."

Lmaooooooooooooooooooooooooooo

ReD eXiLe ms us | April 13, 2020

HighlandPony: And Toyota probably gets their TAC in a box off the shelf at BOSCH or ZF, just like everyone else, from HYUNDAI to MERCEDES-BENZ.

howard | April 13, 2020

Too bad Tesla did not get the Adaptive Cruise Control system from GM as it is far superior. With that said I’ll ask again why is that with all the Tesla tech and FSD just around the corner.........? Before someone else mentions it is a discontinued car no less, is better.

lbowroom | April 13, 2020

So your question is why the adaptive cruise is “better” on your Volt. What kind answer do you think anyone here can give? I suspect what you really want to hear is an acknowledgment that it is better.

Anyway, I suspect it’s because it only has the ability to track the car directly in front of it. Limited scope of functionality makes the task simpler. Good job GM. If you want a different answer, ask a different question.

howard | April 13, 2020

lbowroom, So your answer is the technologically advanced Tesla cannot match the functionality of the simpler Volt when it comes to adaptive cruise control. Why exactly, because the Tesla is tracking to many things to do the simpler task correctly. In others words Tesla’s broader scope of functionality is inferior/not capable to perform the simpler task of adaptive cruise. Guess you are right, Better job GM. There is no different answer, is there? At least none has been given other than deflection and excuse. Been waiting some 18 months for that magical update. Honestly I am trusting it will eventually get here. Till then I’ll enjoy the lack of alarms getting into my car. There’s something.

WW_spb | April 14, 2020

Howard, that's your opinion. And mine is Tesla's Autopilot is better.

Joshan | April 14, 2020

Having never driven a bolt, I cannot comment on that comparison.

But the ACC in my Acura RDX is not comparable to the Tesla TACC at all. I have to intervene far more often, and by far I would guess 10-20x more often.

howard | April 14, 2020

WW_spb Howard, that's your opinion. And mine is Tesla's Autopilot is better.

We are not talking about AP or NOAP or future FSD. We are talking about simple adaptive cruise control. TACC in Tesla's vernacular.

I drive both the Volt and the Tesla back to back and the Tesla is nowhere as good. I don't even use the adaptive cruise on the Tesla. Period. I try it each release and that is it.

Respectfully if you have not driven a 2019 Volt with adaptive cruise you really don't know what you are missing much less talking about.

There is a good bit about my purchase of the M3 that I own but I bought it with what I thought was adaptive cruise. What it came with was some type of "beta" adaptive cruise apparently based on trying to achieve FSD. It stinks.

WW_spb | April 14, 2020

Still that's just your opinion. Not a fact.

howard | April 14, 2020

WW_spb | April 14, 2020
Still that's just your opinion. Not a fact.

You are absolutely correct. It is my opinion based on direct experience with both cars.

WW_spb | April 14, 2020

I have adaptive cruise on my SUV and we had it on my wife's Mazda Cx9. And I like model 3's better still. Based on my experience. Wanna continue?

howard | April 14, 2020

Sure, if you are ever in the Phoenix area I am happy to let you experience the difference. I am also happy for you that you like it better.

ChrisM3CH | April 27, 2020

In countries like Switzerland or Germany TACC is not usable in some parts. In particular bicycle lane markings as common in Europe, missing lane markings or non US markings cause this to occur more often than not and make the feature hard, if not impossible, to use.

Not having CC is a big issue here in Switzerland and disabling the adaptive feature would be more than welcome. Deciding between dangerous TACC and no CC at all is not a solution in my opinion. Since normal cruise control was available prior to the inclusion of AP in the base package I would assume it's not too hard to add it back in and make a lot of current and future customers happy.

Please, give us normal cruise control back.

M-A-B-MCMLXXX | April 27, 2020

"Respectfully if you have not driven a 2019 Volt with adaptive cruise you really don't know what you are missing much less talking about."

They must have made a drastic change for the last two model years; my 2017 Volt's cruise was in no way better than my M3's cruise.

Joshan | April 27, 2020

Can we stop comparing to a car that is not even in production any longer? It was so amazing that GM cancelled it.

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