Random TACC max speed decreases

[halfricanguy]

Hello all, I was curious as to whether this was normal behavior or what may be causing this.

I am on the EAP trial and have had a few phantom braking issues, but most notably, I was driving along a 65 mph stretch of highway with no cars in front of me. TACC was on but Autosteer was off. My speed offset is set to +12 and I had the cruise set to 77.

All of a sudden, my set maximum TACC speed decreased to 50 seemingly out of nowhere. The screen still indicated that the road’s speed limit was 65 so there were no changes there. Luckily I was prepared to reaccellerate, but does anyone know why this happens? It’s a behavior that doesn’t happen with regular cruise control. If I wasn’t prepared to speed back up I could have gotten rear ended from the sudden speed decrease. Not very reassuring.

 

[RedModel3]

Day or night? I've had this happen a couple of times during the day when I come to an overpass that throws a shadow. It's almost like the sensors think it's something I might hit. Yeah, it's not cool. It doesn't happen with regular cruise control probably because most standard CC systems are mechanical and don't use sensors.

 

[halfricanguy]

Thanks for the response, yeah I wanted to see if it was a common occurrence even every once in a while. It was day and I actually do think a couple of times were due to overpass shadows, maybe even just the way the car/road was angled towards the overpass that may have confused the camera or sensors. I also just found this similar discussion here where some speculated that the car may have thought it was on an off ramp or side road.

 

[swaltner]

The times I have seen the actual cruise control speed drop (and not from phantom braking for shadows or signs on overpasses) are limited to when I'm on highway interchanges. When on an ramp switching from one highway to the next, the car will automatically slow down based on the tightness of the curve ahead. It generally slows to a point slightly above the posted speed for the curve.

This doesn't sound like your situation since you don't mention being on a highway interchange, but it is one place that the Model 3 will slow down automatically.

 

[Msjulie]

A black trash bag was blowing on the far right lane, us in the center - the car reacted somewhat abruptly even though the bag was blowing off to the right - so it can be confused by things a person knows is no concern.

 

[Krugerrand]

I’ve had the car react like the OP is describing to a crow flying past my bumper, which was annoying because crows are 5 points a piece and I was only 2 points from taking over the lead.

 

[North75]

I’ve noticed this behavior a number of times as well. Unfornuately it usually surprises me so I haven’t fully been able to try to figure out if there is some kind of common scenario taking place.
My recollection is that sometimes it has occurred when driving past an interchange but I wasn’t taking it. I was just continuing straight. Once or twice I’ve been able to tap the speed limit sign to quickly reset the max speed to the speed limit.

On a related note I’m still a bit confused about how the max speed is supposed to change automatically when I actually am exiting at an interchange. Sometimes it seems to automatically lower the speeds on an exit ramp so you don’t have to disengage TACC, but other times it will just go full speed into a ramp without slowing down. I usually chicken out and touch the brakes in these cases.
It works best when following another car as it will slow down as the other driver does.

 

[boriszima]

I noticed only when speed limit changes, car slows down as it should. Also if car freaks out, things there is an object, will start braking.

 

[C_A_Braun]

Like this? 20180614_180934.mp4

This is on I210 in Pasadena CA near JPL and is very easily repeatable. It will happen in both of the 2 right most lanes of the freeway and the speed limit is 65. There are no over passes or shadows.

I have heard about every excuse from Tesla known to man as to why this happens. The only excuse that makes any sense to me is that there is bad GPS data for that area and the car suddenly thinks that I am on the surface streets below or beside the freeway.

 

[Boourns]

My experience was similar to @C_A_Braun's. One day, going up the same road I take every day home from work, my car thought I was maybe a half mile northeast of where I actually was. So, rather than the 65 mph highway I was on, it thought I was on side streets and limited by TACC speed to 50. This only happened to me once, though.

 

[jsmay311]

Like this? 20180614_180934.mp4

This is on I210 in Pasadena CA near JPL and is very easily repeatable. It will happen in both of the 2 right most lanes of the freeway and the speed limit is 65. There are no over passes or shadows.

I have heard about every excuse from Tesla known to man as to why this happens. The only excuse that makes any sense to me is that there is bad GPS data for that area and the car suddenly thinks that I am on the surface streets below or beside the freeway.

Interesting. It loses the speed limit sign on the right part of the screen for the few seconds there when the target speed drops.

 

[halfricanguy]

Like this? 20180614_180934.mp4

Thank you all for your responses! This is exactly the behavior I was describing. Luckily it hasn’t been that aggressive for me, but a drop to 45 is pretty dramatic. Do you know if it happens to you while traveling in the left most lanes? I think I’ve usually been on the right side of the road so it may be related. I try to submit bug reports when it happens but don’t know how much good it does.

 

[C141medic]

Hello all, I was curious as to whether this was normal behavior or what may be causing this.

I am on the EAP trial and have had a few phantom braking issues, but most notably, I was driving along a 65 mph stretch of highway with no cars in front of me. TACC was on but Autosteer was off. My speed offset is set to +12 and I had the cruise set to 77.

All of a sudden, my set maximum TACC speed decreased to 50 seemingly out of nowhere. The screen still indicated that the road’s speed limit was 65 so there were no changes there. Luckily I was prepared to reaccellerate, but does anyone know why this happens? It’s a behavior that doesn’t happen with regular cruise control. If I wasn’t prepared to speed back up I could have gotten rear ended from the sudden speed decrease. Not very reassuring.

I’ve experienced the exact opposite today. Only TACC enabled without auto steer. Traveling at 50MPH (with gps indicating 50 on the top right of the display). No one in front of me. Speed limit of the road drops to 35MPH (gps also picked up the change and reflected 35MPH on the right side of display) however; the TACC did not adjust and car remained at 50MPH until I had to brake to slow down to the posted speed limit.

Also when going around curves with only TACC enabled the car is not slowing down whatsoever as the manual indicates that that’s what should occur.
“Traffic-Aware Cruise Control also adjusts the speed as appropriate when entering and exiting curves.”

 

[jsmay311]

I’ve experienced the exact opposite today. Only TACC enabled without auto steer. Traveling at 50MPH (with gps indicating 50 on the top right of the display). No one in front of me. Speed limit of the road drops to 35MPH (gps also picked up the change and reflected 35MPH on the right side of display) however; the TACC did not adjust and car remained at 50MPH until I had to brake to slow down to the posted speed limit.

Also when going around curves with only TACC enabled the car is not slowing down whatsoever as the manual indicates that that’s what should occur.
“Traffic-Aware Cruise Control also adjusts the speed as appropriate when entering and exiting curves.”

As I understand it, what you’ve described is the “normal” operation. There’s no limit on TACC set speed when you’re not also using Autosteer/Autopilot, so it won’t automatically reduce the set speed based on changing speed limits.

Same for when driving around curves. It may reduce speeds when on Autopilot/Autosteer, but not TACC by itself. Since that sentence in the manual is missing that hugely important caveat, I’m pretty sure it’s flat-out wrong. (If anyone has observed TACC-by-itself slowing the car down heading into curves, please correct me.)

It’s un-freaking-believable that Tesla allows sloppy mistakes like this to get into official published documents, especially on something safety related. It’s shocking to me — as both an owner and as an engineer.

 

[C141medic]

As I understand it, what you’ve described is the “normal” operation. There’s no limit on TACC set speed when you’re not also using Autosteer/Autopilot, so it won’t automatically reduce the set speed based on changing speed limits.

Same for when driving around curves. It may reduce speeds when on Autopilot/Autosteer, but not TACC by itself. Since that sentence in the manual is missing that hugely important caveat, I’m pretty sure it’s flat-out wrong. (If anyone has observed TACC-by-itself slowing the car down heading into curves, please correct me.)

It’s un-freaking-believable that Tesla allows sloppy mistakes like this to get into official published documents, especially on something safety related. It’s shocking to me — as both an owner and as an engineer.

Thank you for that. Your response makes absolute sense now. And you’re right, that is a very sloppy mistake by Tesla especially in the owner’s manual. I’d think it would be an easy correction to make since the manual is in digital format.

 

[myxsoma]

Hi, I know this one's from a couple months back but you got me to make my first post, yippee. Just FYI, I know from experience that the TACC does slow you for corners even if you are steering, it has done it for me on back roads where there was no line to use for autosteer. It will only do it when it's a significantly sharp corner enough to warrant it. I've never been too clear on if it uses GPS to know about upcoming sharp corners or if it only uses the field of vision/cameras/radar. It def will slow you say, from 40 to 30 going around a corner, regardless of if it's in autosteer or not. Just my exp, others may vary.

 

[BlueCarNut]

Similar to the OP and others, I've experienced a sudden TACC deceleration near an overpass. In my case, I was going over the overpass, so maybe the car suddenly decided to use the speed limit of the road below? In any case, it was surprising, but luckily there was no traffic around and it seemed fine after transiting the overpass.

 

[lolder]

I’ve experienced the exact opposite today. Only TACC enabled without auto steer. Traveling at 50MPH (with gps indicating 50 on the top right of the display). No one in front of me. Speed limit of the road drops to 35MPH (gps also picked up the change and reflected 35MPH on the right side of display) however; the TACC did not adjust and car remained at 50MPH until I had to brake to slow down to the posted speed limit.

Also when going around curves with only TACC enabled the car is not slowing down whatsoever as the manual indicates that that’s what should occur.
“Traffic-Aware Cruise Control also adjusts the speed as appropriate when entering and exiting curves.”

NOA is what slows the car on ramps. With only TACC you can set any speed and it's not limited to 5 mph above the data base ( not GPS ) speed in the upper right corner. TACC will not slow you as the data base speed changes, only EAP and NOA will do that.

 

[jsmay311]

I discovered that this happens in a repeatable fashion on an interchange in the Chicago suburbs... westbound I-290 going onto westbound I-88 around Hillside.

Not that there’s ever any legitimate or acceptable reason to suddenly change the set speed for non-AP TACC without the driver’s input (*IMO*), but in this spot there’s not even any sharp curves or changes in speed limit or anything like that.

Yet, within a span of maybe 1/2 mile it forces your TACC set speed down to 50mph THREE TIMES IN A ROW. (For example: I’m cruising along at 65mph in TACC when suddenly the set speed drops to 50mph with no warning. I quickly reset it back to 65mph. Seconds later it drops to 50mph again. I reset it to 65mph. Seconds later it drops to 50mph again. I reset it again to 65mph.

WTGDF. This is f***ing unsafe and unacceptable and stupid.

(Side note: I tried submitting a bug report, but the bug report feature is such a piece of sh*t in and of itself that it only gives you like 5 seconds to talk before cutting you off... it’s basically useless. What dumb sh*t all around.)

 

[halfricanguy]

Very disheartening to see this hasn’t been resolved. I just finished a cross country trip. Although it’s not a common occurrence, it only takes one time while being tailgated and caught of guard for this to be a recipe for disaster.

There’s a place on your Tesla account under Manage your car to report problems/provide feedback. Please keep sending these in so they get the message