Hard braking with TACC in stop-n-go traffic

[USMC_Mustang]

I noticed the same thing fairly recently. I've found that changing from 1 car-length-following to 2 will apply more moderate braking. But of course, in stop-n-go traffic, that also means everyone and their brother will cut in front of you.

 

[sevenout]

To follow up following the SvC repairs... I can say that the front coil replacement that they did has had no effect on the sound happening. The few times I have heard it have not been super loud like before but that may simply be due to the conditions as the loudness has varied in the past. I'll keep monitoring things as I get more rush hour driving time in.

 

[Nitemare3219]

And it's also harder on the brake pads. I notice this with AP as well. Gone are the days when after a few years, there would be hardly any brake wear on the callipers, now with AP and and TACC, the pads wear out more which means Tesla makes more when you bring the car in for replacement of the brakes!

Eh I disagree. This car is never hard on brakes, even if AP slams on them occasionally at low speed (not much effort required to stop the car at that point). Brake pads are also incredibly easy to change (at least on the front).

 

[Viking1]

Yes. For the way I drive AP waits too long to start slowing with traffic stopped ahead. I've even double tapped the cruise control multiple times to get it to slow sooner. I'm sure that is not what Tesla intended. It would be better if Tesla offered some setting for little-old-lady to indy driver. Better yet, if the car could watch my driving for a while and adjust to my way of driving. That would be ultimate.

 

[FlyingCookie]

I've noticed this on my loaner. AP seems to wait till the last second to brake, and then brakes very hard. I've also found if I gently press the accelerator and then let off, i can hear this sound as AP slams on the brakes as I'm now closer to the car in front of me than it would like for me to be. I didn't think much of it, as this is my first experience with AP for any length of time, though I can see where it would be worrying when it suddenly starts with a firmware update.

AP also just brakes hard in general... I can average 290wh/mile in my P85 using regen to do most of my stopping on a ~25 mile trip to work, but the P85D with AP1 engaged seems to average around 380wh/mile due to the hard braking. (This is in Nashville, so lots of long downhill grades that end at redlights or stopped traffic. It's possible to regen down these grades and come to a stop with a light press of the brakes, but AP1 seems to keep on screaming down the road and then pile into the brakes right at the end)

 

[darkroommd]

Has anyone else experienced hard braking by TACC during stop-n-go traffic? For me, this started with 2017.34 and has persisted with 2017.40.1. As cars begin to slow to a stop, the car will suddenly hard brake and come to a stop. I'm only going maybe 1-2 MPH when this happens but it is abrupt when it does. It does not happen every time either. Half of the time it comes to a nice smooth stop. Also, when it does hard break, I also hear a fairly loud machine gun like sound coming from the front of the car. Could this be ABS? Have never heard that sound before except when this happens. Not sure if I should schedule a service call.

Yep exactly the same for me.

Can't say it has been related to any particular update...it has been present since brand new 3 months ago...currently on 2017.34. For some reason, the update to 2017.42 has failed, even when they tried to do a manual push.

Service appt this week.

 

[darkroommd]

Here are some videos I took where I was able to capture the sound.

#1 - You can hear the sound just as the speedometer hits 12mph. It's very short but that's when TACC decided it needed to hard brake due to the traffic in front of me coming to a stop.

#2 - This one is very short but you can clearly hear the loud judder of the brake pedal. This is a stop-n-go event. Start at zero and go up to 2mph and then hard brake back to zero.

#3 - This one is where AP had drifted way too close to the left of the lane and was starting to encroach on the traffic to my left. Eventually TACC had to hard brake just as the proximity alarm chimed. The camera moves around a bit because I was worried I was going to have to take over due to how close I was getting to the cars on my left.

Thank you for these videos!!! This may save me a lot of time at my service appointment this week.

 

[thatisug]

To follow up following the SvC repairs... I can say that the front coil replacement that they did has had no effect on the sound happening. The few times I have heard it have not been super loud like before but that may simply be due to the conditions as the loudness has varied in the past. I'll keep monitoring things as I get more rush hour driving time in.

Hey Sevenout -- Curious if you had any further updates on your situation? I have had Zero luck, and now with the latest 2017.44 release, it seems the AP / TACC is loving the brakes even more so the sound is occurring more frequently.

 

[sevenout]

Hey Sevenout -- Curious if you had any further updates on your situation? I have had Zero luck, and now with the latest 2017.44 release, it seems the AP / TACC is loving the brakes even more so the sound is occurring more frequently.

Basically no improvement since the SvC repair. The sound is still happening. Personally I think it’s the brake pedal. I can make the sound happen by just lifting my foot off the brake really fast. My foot typically pushes down on the brake pedal on the right side instead of square in the middle. When I lift my foot off I can hear the same sound. Try it and left me know if you get the same thing.

 

[Nitemare3219]

Here are some videos I took where I was able to capture the sound.

#1 - You can hear the sound just as the speedometer hits 12mph. It's very short but that's when TACC decided it needed to hard brake due to the traffic in front of me coming to a stop.

#2 - This one is very short but you can clearly hear the loud judder of the brake pedal. This is a stop-n-go event. Start at zero and go up to 2mph and then hard brake back to zero.

#3 - This one is where AP had drifted way too close to the left of the lane and was starting to encroach on the traffic to my left. Eventually TACC had to hard brake just as the proximity alarm chimed. The camera moves around a bit because I was worried I was going to have to take over due to how close I was getting to the cars on my left.

I've had sounds exactly like video #1 several times from even moderate activation of the friction brakes with AP. Haven't noticed a judder like in video 2, just the extended thud sound. Heard it once the other day when I was flooring the accelerator from low speeds which was odd and may have been unrelated. My guess it's is the system that is manually activating the friction brakes at a higher than usual strength. Even on several ICE vehicles from Dodge/Jeep I've previously owned with adaptive cruise, a hard brake by the system would create a similar noise. Seems like Tesla needs to do some work on the braking. My car is set to a following distance of 4 almost all the time, so I'm not too close and yet it still brakes abruptly sometimes.

 

[Jlittlefield]

Noticed the same hard braking and “chatter” (like abs) today in stop and go traffic with distances set at 1-2. Software version 2017.44

 

[Cirrus MS100D]

Noticed the same hard braking and “chatter” (like abs) today in stop and go traffic with distances set at 1-2. Software version 2017.44

I wear sandals often and have actually felt the brake pedal “juddering” (or chattering?) when this sound occurs by having it hit my toes, so seems like it’s just weird brake pedal (mis)application “by” TACC.

 

[viper2ko]

Just came across this thread. I noticed these exact sounds when autopilot brakes in traffic. What has everyone been doing about it?

 

[THXULTRA]

I have noticed this as well. seems the car brakes later then I would (I try to use the regen braking as much as I can then use the regular brake for the last bit) and really hits the brakes hard in traffic. Especially if a car ahead is turning. Also noticed that it takes a long time for the car to go again if the car in front of me turns.

 

[bob_p]

Have had this issue with TACC since picking up our S 100D in March.

In heavy traffic, TACC is very useful - maintaining speed and spacing automatically.

But, if the car ahead slows down rapidly, TACC seems to react too slowly - and then does heavy braking to slow down - causing the sound. Without TACC, in the same conditions, I'm able to slow down without having to heavily apply the brakes.

So this is a case where TACC appears to be performing worse than a human driver. While TACC is using the brake to successfully maintain spacing and avoid hitting the car in front, it is doing so by using more braking (rather than regen braking).

I wonder...

Human drivers can see the brake lights come on - not only for the vehicle immediately in front - but also the vehicles further ahead. By observing the brake lights, a human driver's response time may actually be shorter than TACC - if TACC is relying 100% on detecting a change in the spacing to the car immediately in front - and because of that, TACC has to brake faster than a human driver.

While EAP/FSD will eventually be looking for speed limit signs, stop signs, stop lights, ... - will the software also be looking for other cues that human drivers use - such as turn signals, brake lights - or the sound of emergency vehicles/train crossings? These cues provide human drivers a warning about changing conditions - before they happen - if the AP software isn't looking for these cues and is relying 100% on tracking vehicle movement, then AP may not be as safe as a human driver in some situations...

 

[yukic1683]

I have the same issue, it happen every time during stop-and-to traffic with sudden slow down. Recorded the sound and went to Service Center. They could not reproduce the sound. Told me the car is OK, I have to live with it.

 

[scottf200]

Here are some videos I took where I was able to capture the sound.
#2 - This one is very short but you can clearly hear the loud judder of the brake pedal. This is a stop-n-go event. Start at zero and go up to 2mph and then hard brake back to zero.

I just talked to my service center about this exact sound in your #2 today. I have a June 2017 built Model X with 2017.50.3 firmware. I have over 20K AP miles (36K total) on my previous Model X and do not recall hearing this sound before.

 

[sevenout]

I just talked to my service center about this exact sound in your #2 today. I have a June 2017 built Model X with 2017.50.3 firmware. I have over 20K AP miles (36K total) on my previous Model X and do not recall hearing this sound before.

After taking those videos and then taking my MS to the SvC, I gave them the videos so they could possibly identify the problem. They ended up changing out on of the front struts but that has not solved the issue. Since then, I've come to think that the noise is coming from the brake pedal itself. I've head a very similar noise just by taking my foot off the brake really fast. I think TACC is applying brake pressure in pulses and that is causing the brake pedal to vibrate. This is just a guess.

 

[scottf200]

After taking those videos and then taking my MS to the SvC, I gave them the videos so they could possibly identify the problem. They ended up changing out on of the front struts but that has not solved the issue. Since then, I've come to think that the noise is coming from the brake pedal itself. I've head a very similar noise just by taking my foot off the brake really fast. I think TACC is applying brake pressure in pulses and that is causing the brake pedal to vibrate. This is just a guess.

Thanks for the follow up. I actually just sent my SC the #2 video link above and let them know this is the noise I hear regularly. I had a 2016 X before my 2017 and it absolutely did not do this. In theory, software changes could have cause it (brake? software) to work differently. I don't know if there was hardware changes around this. I had a AP1 X before and this X I have now is AP2.

 

[yukic1683]

After taking those videos and then taking my MS to the SvC, I gave them the videos so they could possibly identify the problem. They ended up changing out on of the front struts but that has not solved the issue. Since then, I've come to think that the noise is coming from the brake pedal itself. I've head a very similar noise just by taking my foot off the brake really fast. I think TACC is applying brake pressure in pulses and that is causing the brake pedal to vibrate. This is just a guess.

I think you are right. Yesterday, I managed to make it happen from brake pedal by sudden stop and release very very very fast. I believe it is AP software during stop-and-go try to do stop and go within less then 1 second (faster than our feet response time). My concerned is, is it bad for the brake pedal?