Is the phantom braking with TACC or something else?

[GLM3]

Sorry, I'm new to the forum and I am still trying to get to know my Model 3. I've now experienced this multiple times. Traveling at highway speeds (on an Interstate highway) I've experienced the TACC automatically change the set speed from the current setting somewhere near 70 mph to 55 mph or 40 mph and immediately slow to those speeds. I haven't taken the time to see if it would automatically adjust up because I have been in traffic and don't want to cause an accident. I believe I've been near exit ramps each time it has done so and it seems the car believes I have taken the exit, or it is adjusting to the limit of the road I'm crossing.

Any thoughts on how to avoid the problem other than not use cruise control?

Thanks in advance,

GLM

 

[Knightshade]

Phantom braking is when the car slows down for no obvious reason. This isn't that.

It's slowed down for a very obvious reason- it thinks the speed limit has significantly decreased.

You'd probably need to experiment a bit further to try and figure out if it simply has incorrect speed limit data in the maps (which is where it gets its speed limit info from) or if for some reason it thinks you're on a different road all of the sudden that has a different limit.


There's a local road near my house for example that I can set TACC to 60 for miles, but beyond a certain point even though the actual speed limit doesn't change, the map data no longer has a listed speed limit so the car drops to 45 by default.

I've never had the "thinks I'm on a totally different road" issue, but I have see a few other suggest they've experienced it certain places.

 

[67King]

Usually means the car does it unpredictably. Sometimes an overpass will cause it. Sometimes a car crossing in front of you, but still a ways away will cause it. But just a change in the speed limit doesn't usually cause what people refer to as "phantom" braking. Now I will say this, there are some places where mine will brake HARD when the speed limit changes. i've learned to just cancel the cruise control in those places so I don't have to deal with it.

 

[GLM3]

Maybe I wasn't clear. I am traveling on the Interstate with a 70 MPH speed limit. The speed limit doesn't change, I haven't exited the interstate, but for some reason, the car immediately slows hard as if it had slammed on the brakes. After this happened a few times I noticed the set point for cruise control had changed. Are you telling me that I need to cancel the cruise control each time I pass an exit or drive over/under a bridge where I cross a secondary road at the risk of immediately slowing by 15 to 35+ mph? Doesn't seem reasonable. This happened four times in a recent 50 mile trip on the Interstate. If others aren't seeing this then maybe service is required.

 

[Knightshade]

Maybe I wasn't clear. I am traveling on the Interstate with a 70 MPH speed limit. The speed limit doesn't change, I haven't exited the interstate, but for some reason, the car immediately slows hard as if it had slammed on the brakes. After this happened a few times I noticed the set point for cruise control had changed.

That means the car thinks the speed limit changed.

As I suggested next step would be figuring out if that's because the map data for whatever bit of road this happens on has the wrong speed limit for some reason (since it's basing its speed limit into entirely on map data) or if it thinks you're on a road other than the one you are actually on.


I suppose one part of that would be see if it's repeatable in the SAME spot (and if it happens regardless of what lane you're in)

 

[focher]

I’ve only encountered this when the system has a “safety speed” set. IfTACC has been set above the speed limit and the car enters a zone with a safety speed set (seen on curves and interchanges) then it will reset to the safety speed. I’ve yet to experience the safety speed being less than the speed limit, though.