Phantom Braking misunderstanding

[acoburn73]

I’ve had my share of so called Phantom Breaking too.

If you pay attention to what’s going on around you, you’ll see it isn‘t phantom at all. Something caused the event.

Nope. I've had several events in the middle of nowhere Kansas on I-70. Sun straight up high noon, no highway mirages, no overpasses, and zero cars around me (very common on that highway in Kansas). The car (enhanced autopilot) set to 77 mph (speed limit 75). Then the event happens. Car decelerates dramatically, without warning, nothing on the screen about obstacles. Turned off the emergency stop for obstacles setting - still happened. Turned off autopilot and just used TACC. Still happened. And when it happened, I finally started paying attention to the speed limit setting on the screen. In all cases the TACC reset the max speed limit to 50 mph. So the car slowed immediately from 77 to 50 mph.

Why? Who knows. There was nothing on the highways around me to trick the car into doing this. We even thought it was LTE signal issues because coincidentally one of the events happened at the same time that the kids lost their tablet streaming signals. But that was likely an anomaly since the other 10-15 occurrences had no linkage to LTE signal dead spots. It got so bad that the engineer in me (I am an aerospace engineering manager) decided to do a full root cause analysis during the trip back to CO from KY. Was totally unable to come up with an quantitative evidence - everything was anecdotal / qualitative, and random, except the 50 mph max speed change. I couldn't identify anything on the road or windshield (thought maybe it was dead bugs, but nope, cleaned windshield at one point, got back on I-70, and 6 minutes later, BAM, 77 to 50 mph deceleration). Service is no help - they just say "your camera test shows all cameras working fine".

I haven't tried AP on this specific car ('21 MYLR) since last summer because it's futile, so maybe they've made some updates. Maybe I'll take it out for a test this weekend given there are rumblings out there that some people are seeing dramatic reduction in phantom events.

 

[acoburn73]

They’re confusing the phantom braking issue (although much less of an issue than before) with the intentional safety feature of slowing down when driving much faster than traffic in adjacent lanes as indicated by the chevrons on the display. For reference from the “Tesla Model Y manual”:

Lots of people trying to tag these events to the obvious cars or obstacles, but there are way too many instances on this forum (and in my experience) where there has been literally no physical thing that the car could possibly have mistaken for an event warranting immediate deceleration.

Few if any birds, at least none around the car during these events (once you have a few phantom braking experiences, you are no longer driving relaxed and are paying attention!)
No bugs on windshield blocking cameras
No mirages
No sun glare or camera blinding
Clean windshield
No cars anywhere
No dramatic up/down hill climbing
Clear lines on the highway
No one in the emergency lanes
No cars entering the highway on an exit ramp
No overhead bridges
No change in speed limit signage
No nearby detectable stop lights or stop signs
And during and after the event(s), zero notification on the screen that the car had to decelerate for some safety/collision avoidance reason

Sure, many people have been able to tie some repeatable, physical thing to their events, and even I have one spot on one particular highway near home and work that always results in a 50 mph max speed reset during autopilot, but the vast majority of my experiences were during a 32 hour round trip road trip across one of the most car-less stretches of highway in the US - from Colorado to KY via I-70 through Kansas.

You know the odd thing about this trip experience? Every single one of the phantom events happened between Limon, CO and Salina, KS, and then again between Salina and Limon. ZERO events happened from Salina through Missouri, Illinois, and into western Kentucky, and zero were from KY to Salina. For anyone that's driven I-70 through Missouri between KC and St Louis. you know well just how much traffic increases as compared to Kansas. And then there are way more trees, hills, exit ramps, overpasses, crappy road lines, and bugs and birds. So to have NO braking events in that area, with all of those possible and REAL obstacles, but having so many in the middle of nowhere western KS, well, is perplexing.

 

[derotam]

Nope. I've had several events in the middle of nowhere Kansas on I-70. Sun straight up high noon, no highway mirages, no overpasses, and zero cars around me (very common on that highway in Kansas). The car (enhanced autopilot) set to 77 mph (speed limit 75). Then the event happens. Car decelerates dramatically, without warning, nothing on the screen about obstacles. Turned off the emergency stop for obstacles setting - still happened. Turned off autopilot and just used TACC. Still happened. And when it happened, I finally started paying attention to the speed limit setting on the screen. In all cases the TACC reset the max speed limit to 50 mph. So the car slowed immediately from 77 to 50 mph.

Why? Who knows. There was nothing on the highways around me to trick the car into doing this. We even thought it was LTE signal issues because coincidentally one of the events happened at the same time that the kids lost their tablet streaming signals. But that was likely an anomaly since the other 10-15 occurrences had no linkage to LTE signal dead spots. It got so bad that the engineer in me (I am an aerospace engineering manager) decided to do a full root cause analysis during the trip back to CO from KY. Was totally unable to come up with an quantitative evidence - everything was anecdotal / qualitative, and random, except the 50 mph max speed change. I couldn't identify anything on the road or windshield (thought maybe it was dead bugs, but nope, cleaned windshield at one point, got back on I-70, and 6 minutes later, BAM, 77 to 50 mph deceleration). Service is no help - they just say "your camera test shows all cameras working fine".

I haven't tried AP on this specific car ('21 MYLR) since last summer because it's futile, so maybe they've made some updates. Maybe I'll take it out for a test this weekend given there are rumblings out there that some people are seeing dramatic reduction in phantom events.

Ok well you just explained the why. This wasn't phantom braking, this was phantom speed limit changing. The car braked to 50 because the car updated the speed limit AND determined it should slow down to match the new(although incorrect presumably) speed limit.(this is in contrast to it changing the speed limit down and sometimes deciding to maintain your TACC speed setting).

Now, why it chose to change the speed limit, that is the question, most likely bad map data, could be mis-applying a truck speed limit(I think this is unlikely however)...maybe something else.

 

[acoburn73]

Ok well you just explained the why. This wasn't phantom braking, this was phantom speed limit changing. The car braked to 50 because the car updated the speed limit AND determined it should slow down to match the new(although incorrect presumably) speed limit.(this is in contrast to it changing the speed limit down and sometimes deciding to maintain your TACC speed setting).

Now, why it chose to change the speed limit, that is the question, most likely bad map data, could be mis-applying a truck speed limit(I think this is unlikely however)...maybe something else.

Today in the same spot it adjusted from my preset speed of 70 mph to 65 mph. Same spot where once it dropped to 50 mph, then 55 mph. So something about that spot makes it want to slow down.

 

[jeffkruse]

It happens to me frequently. I have to quickly step on the accelerator each time. It’s unacceptable. You don’t figure you have to research whether the car you’re buying has working cruise control.

 

[KLam]

Today in the same spot it adjusted from my preset speed of 70 mph to 65 mph. Same spot where once it dropped to 50 mph, then 55 mph. So something about that spot makes it want to slow down.

It could be errors in GPS. Are you near some sensitive military sites. GPS jamming sometimes happens. Are there surface roads running parallel?

 

[David99]

I actually like how FSP is very careful when the lane next to me is moving slow while mine is open. It is a high risk situations. People will try to merge into the empty lane underestimating your speed. I always drive very carefully in those situations and I'm happy to see FSD does the same. There is some substance to the argument that suddenly slowing down is also dangerous.

But actual phantom braking is still very much a thing. It's not very common but happens out of the blue sometimes. Just one of the many reasons I use any kind of self driving feature on freeways only.

 

[derotam]

Today in the same spot it adjusted from my preset speed of 70 mph to 65 mph. Same spot where once it dropped to 50 mph, then 55 mph. So something about that spot makes it want to slow down.

You are right, there is something that is causing the computer to change the speed limit and TACC setting but that isn't phantom braking... Also you just said it happened at the same spot which gives some permanence to the specific braking incident. Without knowing the exact spot at a minimum there would be no way for anyone to really provide much more insight to why it may be happening.

The system changing what value it is changing the speed limit too is interesting as well.

 

[derotam]

It could be errors in GPS. Are you near some sensitive military sites. GPS jamming sometimes happens. Are there surface roads running parallel?

Maybe interference but jamming unlikely. Jamming would be dis-alowed in the US open air without lots of high up approvals. Last year there was a public notice about actual GPS interference testing by the military. GPS Service Interruptions | Navigation Center lists those dates.

GPS interference is more likely in big cities where lots of tall buildings block and scatter the GPS signals which causes errors and loss of accuracy.

 

[enemji]

I don't think it is a good idea to anthropomorphize the car and try to guess what it is thinking and ascribe motives to it,

Humans tend to do that. Take the bible for example and you will see as many explanations as there are priests…. and none of them ever spent a minute with Jesus to actually understand.

 

[PianoAl]

I think we are doomed as humanity to believe any garbage published by news outlets and influencers. I am so disappointed in people now. Am I wrong about this?

Not wrong. Quest for clicks leads to clickbait BS that misleads readers who never learned critical thinking. We are doomed due to a self-perpetuating failure in education.

I figure that it's dumb people who don't understand the benefits of EVs, so that's why there are so many Tesla-bashing articles. Example headline:

"I had to charge my Tesla for an hour just to get home!"

 

[enemji]

I've had several events in the middle of nowhere Kansas on I-70. Sun straight up high noon, no highway mirages, no overpasses, and zero cars around me (very common on that highway in Kansas). The car (enhanced autopilot) set to 77 mph (speed limit 75). Then the event happens. Car decelerates dramatically, without warning, nothing on the screen about obstacles.

That is the perfect description of the environment that causes the Phantom Braking. I believe it is happening because FSD is not observing any vehicles in the environment for a defined period of time. This triggers a safety check slowing the vehicle down rapidly.

 

[derotam]

That is the perfect description of the environment that causes the Phantom Braking. I believe it is happening because FSD is not observing any vehicles in the environment for a defined period of time. This triggers a safety check slowing the vehicle down rapidly.

Except the user stated that it happened at the same spot a second time, which starts to bring in other possibilities.

Your theory is interesting but I don't see any reason why "if no other vehicles for x amount of time then rapidly slow down and ignore the posted speed limit" would be in the logic of the vehicle. Not saying it isn't true but it doesn't make sense.

 

[fholbert]

Maybe interference but jamming unlikely. Jamming would be dis-alowed in the US open air without lots of high up approvals. Last year there was a public notice about actual GPS interference testing by the military. GPS Service Interruptions | Navigation Center lists those dates.

GPS interference is more likely in big cities where lots of tall buildings block and scatter the GPS signals which causes errors and loss of accuracy.

Actually, GPS jamming or interference (not sure of the difference) by the US military is very common. It’s done in short bursts, assume something is being tested. As a pilot, I get an email about scheduled jamming two or three times a month.

 

[fholbert]

I do a fair amount of driving before 4:00am, traffic is really light and I’ve let my MY go to see what it was doing.

Navigation set for destination, cruise control on, nothing more. In Burbank, on the 134 westbound. Nav says to get off at Buena Vista, but I’m going to continue to Hollywood Way. It’s longer, but faster to Warner Brothers’ new buildings. I’m in the second lane from the right, no vehicles within a 1/2 mile.

Suddenly phantom braking! It happened a couple times before I realized the car thought I was taking the Buena Vista off ramp at 75/80 mph. I don’t understand why this doesn’t happen every time I drive past my off ramp. As I said before, instead of cursing the car try to figure out why it reacted the way it did. I think almost all phantom braking had a reason.

 

[derotam]

Actually, GPS jamming or interference (not sure of the difference) by the US military is very common. It’s done in short bursts, assume something is being tested. As a pilot, I get an email about scheduled jamming two or three times a month.

When I say Jamming I mean actual intended jamming, interference could be tossing a bunch of aluminum foil bits in the air that would scatter the signal.

I am curious, what entity puts out these Jamming notices?

 

[fholbert]

When I say Jamming I mean actual intended jamming, interference could be tossing a bunch of aluminum foil bits in the air that would scatter the signal.

That’s called chaf, it was clearly visible on radar, looked like a heavy storm cell. The idea was aircraft could sneak in behind it. I saw it a couple of times when I was an Air Traffic Controller. Don’t think it’s been used for decades.

I am curious, what entity puts out these Jamming notices?

Assume it originates with DOD, but I’m notified by the FAA. A lot of secret stuff goes on in southwestern states, Area 51 type stuff. Flying near to Edwards AFB I’ve hear little things on the comms that’s just weird.

 

[enemji]

Except the user stated that it happened at the same spot a second time, which starts to bring in other possibilities.

I have had those and they appear to be very weird. The car slows down to a stop at one particular point on a road, anytime and everytime. No idea why.

 

[kabin]

It's rumored Tesla uses ghost buster certified cameras. It's not phantom braking, they regularly detect and avoid unsettled spirits in the night. After all, they were human too.

 

[enemji]

Your theory is interesting but I don't see any reason why "if no other vehicles for x amount of time then rapidly slow down and ignore the posted speed limit" would be in the logic of the vehicle. Not saying it isn't true but it doesn't make sense.

Let me help you. Hopefully it makes sense.

If there is no vehicle detected / no change in the within scope surrounding environment, it might mean there is a glitch and the vision processing has been jammed for unknown reasons. That is a disorienting situation and triggers a safety alert as continuing to keep driving would be dangerous.

It is much like a situation when JFK crashed due to lack of visual reference points.