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Phantom Braking theory...need help to test this out


May 11, 2021
Durham, NC
I have it on +0% right now due to nervousness about fsd beta, and I still get phantom braking. It is worse than it was with 32.22 build, where this had improved over 21.3 (I think 21.3 was a vision only branch)…. I am hoping the fsd beta version (fsd 10.2 or 32.25) is simply containing those old bugs from the vision-only branch, and can get some commits from 32.22 to resolve it a bit.
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Sep 12, 2021
Yeah, at 0% didn't help me either.

My drive to the cottage is 1/3 high ways, 1/3 90 km/h two way traffic roads and 1/3 city streets. I used autopilot on the first two. On highways, never had a issue with phantom braking, may be very slight slow down but nothing to put the brakes on. On two ways traffic roads on the other hand, almost every time I met a car while turning right, it would put the brakes, sometime hard. I now push the accelerator in a bit when I see a car approaching in those situations. It prevents or greatly reduces the phantom braking. It still does it for no apparent reason on a straight road with no incoming car though. That's the most annoying one.


Sep 11, 2021
Timaru New Zealand
Just a thought. Phantom braking seems to be an added impulse upon regen slowing. Is it possible that those of us getting vicious phantom braking are so near fully charged that the regen hasn't enough energy and the system defaults (late) to mechanical braking? Chichi is rarely above 80% so does nothing late or sudden.


Nov 27, 2020
Hopefully a useful data point:

Have a Sept 2020 MYLR w/ radar hardware. I have had all the available FSB options turned on (just downloaded the Beta today). I have always had speed limit +5 miles/hr set. I use Chill and Standard. I have not driven over 75 miles per hour since they stopped using radar. I'm on State highways more often than Interstates. Since they disabled radar usage I no longer get unpleasant aggressive phantom braking. I do get slowdowns at what the cars thinks are blinking yellow lights and sometimes when passing bright yellow signs verses standard/darker yellow signs). In places (always the same extact places) where phantom braking used to occur I, instead of phantom braking, get a small red "Forward Collision Warning" displaying towards the bottom of driving visualization.


Mar 6, 2020
Hudson Valley NY, WA state
I bumped this thread so that new FSD beta users would be aware of its discussion. I have no thoughts as to whether the theory posed by the OP explains some aspects of phantom breaking. However, it is good practice with FSD beta to have the speed limit set to zero offset/percent.

Also, using the right scroll wheel to control vehicle speed will be overridden by either speed limit signs or speed limit mapping. This could lead to an unexpected change in vehicle speed.
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Supporting Member
Supporting Member
Aug 8, 2021
Moab, UT
First my apologies if you've already read an earlier version of this post. I originally posted it in a different thread but this thread seems more relevant...

I live in a red rock desert with wide open vistas and many dead straight two-lane highways. I sometimes leave early in the morning to drive 250 miles of mostly wide well-striped two-lane roads to Salt Lake City (and back same day). In that distance we can experience more than 25 instances of severe phantom braking - each way!. Leaving in the dark, oncoming headlights as far away as 200 yards or more (really!) can initiate sudden violent braking dropping speed from 65 mph to 40 mph in less than 2 seconds. Other times approaching bridges, guardrails, highway cuts between earth berms, oncoming trucks (usually dark colored) or sometimes absolutely nothing (obvious) will cause an event. Most, but by no means all, braking events occur in poor lighting or with strong side light shadows such as nearing sunrise or sundown. Flat lighting seems to reduce but not eliminate the incident rate.

I've endeavored to record many "bug reports" and have force-saved dash cam video but nothing out of the ordinary shows in later reviews. I've recalibrated the cameras several times with no apparent effect. A recent software update to 2021.36.5.5 has also had no apparent effect.

So, here's my personal take on what could be behind phantom braking:

1. It would make sense for Tesla's TACC to use the same object recognition algorithms as FSD. When dealing with self-driving I'm sure Tesla is going to be ultra-conservative in their assessment; they don't want to be accused of causing collisions. Hence, braking is deemed preferable to incorrect analysis that could cause a potentially fatal accident. (Although phantom braking can and likely will lead to rear end collisions.)

2. The forward looking cameras used for distance in our MY appear to be spaced no wider apart than human eyes, maybe less. In every other vehicle I've owned with "adaptive speed control" the traffic aware cameras have been spaced upwards of 8"-12" apart. This wider spacing offers far better distance/range analysis. Tesla seems to be counting on their camera quality and range finding technology - but it's not there yet.

Anyway, neither of these conditions are likely to be resolved anytime soon so I end up driving my high tech automobile as if it was 1960. :(
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Burrito Founder
Nov 10, 2011
Mirages and phantoms, the ingredient of Tesla's TACC.

Happens constantly for us too. Turns a pleasant drive into a stressful one. You either have to either check your speed (ie, TACC off) or be ready to accelerate (TACC on).
I really wish Tesla offered a setting for normal CC when you want it. There are times when TACC is useless precisely because it's failing at being a good CC.

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