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Sudden Slowing and Cruise Control Speed Change

MikeNNN

Member
Dec 3, 2019
12
2
USA
I took my first "longish" trip yesterday--200 miles each way up to San Jose to have a hitch installed on my Model 3. On three occasions (twice going up and once coming home) this happened:

My cruise control is set for 9 miles over the speed limit (69, 74 or 79), I'm on a divided highway, and I'm in the right hand lane approaching a passenger side off ramp as the road is gently curving to the right with no vehicles in front of or to my side. I have auto steer turned on and my hand is on the wheel. The car suddenly slows down to the speed limit and my cruise control is reset to the speed limit (e.g, from 74 to 65). As I recall, my auto steer stayed activated.

Any ideas what's causing this before I contact service?

Thanks.
 

NovemberXray

Member
Apr 21, 2016
295
398
Portland, OR
I am not coming up with a good explanation based on your description, however I definitely see this regularly when using navigate with autopilot when approaching an exit or turn, it will slow the car and show the cruise speed setting reduce and then after the maneuver it will go back up.
 

Occhis

Member
May 26, 2019
246
111
Front Royal, VA
I’ve had that happen when on exit ramp the cruise control resets to the speed limit and I’ve always thought that it was a steering angle sensor thing. Curve is too tight for the higher set speed limit, so the system slows it down and resets to the legal posted limit. On an exit ramp that I use regularly, it happens every time.
 

Rottenapplr

Active Member
Apr 6, 2019
1,015
536
LOS ANGELES
I took my first "longish" trip yesterday--200 miles each way up to San Jose to have a hitch installed on my Model 3. On three occasions (twice going up and once coming home) this happened:

My cruise control is set for 9 miles over the speed limit (69, 74 or 79), I'm on a divided highway, and I'm in the right hand lane approaching a passenger side off ramp as the road is gently curving to the right with no vehicles in front of or to my side. I have auto steer turned on and my hand is on the wheel. The car suddenly slows down to the speed limit and my cruise control is reset to the speed limit (e.g, from 74 to 65). As I recall, my auto steer stayed activated.

Any ideas what's causing this before I contact service?

Thanks.
I get this bug toooooo. It’s super annoying because you drop 10 miles if you are not paying attention. You could get rear ended. I think at this point it’s a bug. I’ve only experience it for the last 3 months and I’ve owned the car longer. There’s no fix right now until tesla updates the software.
 

thewishmaster

Member
Jun 4, 2018
671
570
California
There is a straightaway near me where my car always drops to 40 mph, with the limit very clearly still set to 65mph. I thought it was a GPS error, but I realized that most of the time I’m in the lane that merges into another lane a few hundred feet ahead of where my car slows down.

I bet your slowdown and mine are related to the fleet speed feature where the car slows down to some average speed of other teslas that have passed through there. Its usually on curves though, where you can watch the set speed gradually descend to something like 55 or less, and reset to your set maximum after the curve.
 
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Rottenapplr

Active Member
Apr 6, 2019
1,015
536
LOS ANGELES
There is a straightaway near me where my car always drops to 40 mph, with the limit very clearly still set to 65mph. I thought it was a GPS error, but I realized that most of the time I’m in the lane that merges into another lane a few hundred feet ahead of where my car slows down.

I bet your slowdown and mine are related to the fleet speed feature where the car slows down to some average speed of other teslas that have passed through there. Its usually on curves though, where you can watch the set speed gradually descend to something like 55 or less, and reset to your set maximum after the curve.
So it only happens on those areas and not in other areas?
 

rjt!

Member
Sep 8, 2019
9
6
Atlanta, GA, USA
There is a spot here in Atlanta where something like this happens to me every time - I'm cruising along at 60 in a 55, and suddenly the cruise set speed drops to 35 (!!) and of course regen kicks in and the cars behind me (well, there were cars before Corona became more than just a beer) get very unhappy that I am suddenly slowing down.

Now I've been past it enough I've reached the tentative conclusion that this happens just as I am reaching a specific overpass, and the car thinks the speed limit has dropped from 55 to 35, the speed limit on the road I am driving over (thus resetting the cruise speed) before I get past the overpass and the speed limit is back to 55 - faster than I can react, at least. So what I see is the cruise at 35 and the speed limit at 55. This is, of course, all just speculation on my part.

This sounds to me like a maps bug. I have no idea how to report this.
 
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shikataganai

Member
Apr 8, 2020
18
7
Denver
I've noticed several such bugs/"features":

1) Sensing a curve ahead or a zone marked as an off- or on-ramp, then it'll slow to the speed limit if not below yet.

2) Random jumpiness due to shadows on the road.

3) Consistent lowering of the cruise speed limit to 40 or 30 mph when its GPS maps have incorrect or missing speed limit data. This happens consistently on one stretch on my route to work, so I just drive manually until I pass it.

For issue #3 you all should report where it happens: [email protected] . I've never gotten a response but at least hope that someone reads those reports...
 

Mrbrock

Active Member
Mar 26, 2020
1,007
694
Napa, CA
As far as I know, Autosteer with cruise control only works 5 miles per hour above the posted speed limit. I have been able to go faster with autosteer by pressing on the accelerator but letting the car do it’s thing it will slow to 60 in a 55 and show a message on the screen. Could your car have been doing this?
 

rincewind

Member
Nov 5, 2019
558
309
London England
When autopilot is engaged, when taking an off ramp the Autopilot will reduce speed to that of other Tesla's that have recently been at that junction. It's in the manual:

When enabled while on a highway interchangeor off-ramp,Traffic-Aware Cruise Control mayreduce your set speed in 5 mph (5 km/h)increments – to as slow as 25 mph (40 km/h)– to better match the reported speeds ofother Tesla vehicles that have driven at thatspecific location. To override this and continuecruising at your set speed, tap the acceleratorpedal or touch the plus (+) or minus (-) buttonon the touchscreen. The new set speed is maintained for the duration of the interchangeor off-ramp (unless you override it or cancelTraffic-Aware Cruise Control). After theinterchange or off-ramp, the set speed mayrevert or change as necessary based on thenew location.
 
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Knightshade

Well-Known Member
Jul 31, 2017
13,241
22,096
NC
As far as I know, Autosteer with cruise control only works 5 miles per hour above the posted speed limit. I have been able to go faster with autosteer by pressing on the accelerator but letting the car do it’s thing it will slow to 60 in a 55 and show a message on the screen. Could your car have been doing this?


On a real freeway it'll go as fast as you want above the speed limit up to 90 mph max.

On roads it's not actually intended for use on though it's limited to 5 over... or a flat 45 if it doesn't have a known speed limit in the database)



When autopilot is engaged, when taking an off ramp the Autopilot will reduce speed to that of other Tesla's that have recently been at that junction. It's in the manual:

When enabled while on a highway interchangeor off-ramp,Traffic-Aware Cruise Control mayreduce your set speed in 5 mph (5 km/h)increments – to as slow as 25 mph (40 km/h)– to better match the reported speeds ofother Tesla vehicles that have driven at thatspecific location. To override this and continuecruising at your set speed, tap the acceleratorpedal or touch the plus (+) or minus (-) buttonon the touchscreen. The new set speed is maintained for the duration of the interchangeor off-ramp (unless you override it or cancelTraffic-Aware Cruise Control). After theinterchange or off-ramp, the set speed mayrevert or change as necessary based on thenew location.


I was today years old when I learned this. And I'm someone who has read the manual more than a few times.... guessing this was added relatively recently but too lazy to see if the wayback machine can tell me or not.
 

Mo City

Active Member
Jul 17, 2016
1,910
11,883
near Houston
Don't bother contacting service. It's probably your car thinks the speed limit suddenly dropped 10-15 mph. Will you be traveling the same route anytime soon? If so, check for this next time it happens.

On southbound Highway 288 in Houston approaching BW8, my car thinks the speed limit changes from 65-50-65-50-65 within ~5 blocks. It's madness.

Whatever GPS database Tesla is using should have an algorithm to check for, investigate and correct obvious errors like this.
 

ElectroFish

Model 3 Perfromance
Nov 12, 2019
67
48
miami
On my route home I go from 75 mph to 45 while on the highway . Only happens when I drive in the right lanes . Really annoying and dangerous
 

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