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Cruise control set speed changing on its own

Cruise control set speed changing on its own

Twice yesterday on the highway, the cruise control set speed changed on its own.

I wasn't using self driving (no auto steer or autopilot), just plain old cruise control. I was on a highway with a speed limit of 100km/h, and my cruise was set to 115km/h. Twice, the set speed dropped on its own to 100km/h. I didn't touch anything, didn't accidentally change the speed myself, and it's not the "phantom braking" problem which I also did experience a few times in the past. The speed of the cruise control changed.

I could understand if I was on autopilot that maybe, and just maybe, it mistakes the car for being on the adjacent road with a lower speed limit and it would "correct" itself, but I was just on cruise control in the middle of a straight line deserted highway.

Has anyone ever experienced anything similar? Thoughts?

stingray.don | 16. februar 2020

Check your settings. TACC will adjust speed based on your offset to the speed limit. So if the speed limit changes so will your cruise control speed. See the owners manual for details.

Sarah R | 16. februar 2020

It does that.

You'll probably notice that it does it at the same places every time. Because TACC tries hard to obey traffic laws. It's probably getting the speed zone information from Google Maps, which means there's a non-zero probability that it contains an error.

DiminishedSeventh | 16. februar 2020

@stingray.don TACC will NOT adjust your speed based on the speed limit. Directly from the manual:

“Warning: When cruising at the speed limit, the cruising speed does not change when the speed limit changes.”

TACC will only slow you down if it detects a slower vehicle in front of you or when approaching a curve. Sometimes it will think you’re on a frontage road instead of the highway. That would be quite dangerous if TACC were to auto-adjust your speed if you were on a 75 mph highway and all of sudden drop down to 35 mph due to some variance in the GPS/maps.

OP, if you didn’t accidentally nudge the scroll wheel, your set speed should not be changing. Do you have a max speed limit set?

stingray.don | 16. februar 2020

I stand corrected. On AP, you are limited to 5 MPH over the speed limit on city streets. This can cause the speed to change and remain on AP. I don't use TACC without autosteer so didn't realize it was different with only TACC.

FISHEV | 16. februar 2020

"Twice yesterday on the highway, the cruise control set speed changed on its own."

It will change set speed up and down on it's own causing unintended accel ( there's a big lawsuit brewing on this) and decel from the adaptive cruise.

Adaptive cruise should only be doing what drive tells it not changing speed on it's own. That bug is from FSD requirements making AP dysfunction.

DiminishedSeventh | 16. februar 2020

Let’s do how many threads @fishev will post this false information in. For the third time now, quoted from the manual:

“Warning: When cruising at the speed limit, the cruising speed does not change when the speed limit changes. If your driving speed is at or below the new speed limit, move the lever up to cancel Traffic-Aware Cruise Control, then move it back down again to re-initiate and cruise at the new speed limit.”

FISHEV | 16. februar 2020

"When cruising at the speed limit, the cruising speed does not change when the speed limit changes."

That's why so many owners are surprised when it does in fact change the cars speed based on what AP thinks is the speed limit.

FISHEV | 16. februar 2020

Easiest test is simply exiting the highway at 70mph. Teslas adaptive cruise will drop the speed limit to 50 mph even though driver does not want or expect it do that.

DiminishedSeventh | 16. februar 2020

“Easiest test is simply exiting the highway at 70mph. Teslas adaptive cruise will drop the speed limit to 50 mph even though driver does not want or expect it do that.”

False. That is in no way an accurate “test”. When approaching a curve or off-ramp, the vehicle will decelerate. This is documented and expected behavior for anyone that knows the proper operation of the vehicle. Just because YOU didn’t expect it because YOU didn’t read the manual, doesn’t make the vehicle at fault.

“When enabled while on a highway interchange or off-ramp, Traffic-Aware Cruise Control may reduce 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 of other Tesla vehicles that have driven at that specific location.”

I drive everyday on a highway that transitions from 55 mph to 70 mph and never once have I had the vehicle automatically change speeds.

teslamazing | 16. februar 2020

I don’t know why fish is even commenting on TACC when he or she doesn’t even use it based on its behavior.

FISHEV | 16. februar 2020

" I don’t know why fish is even commenting on TACC when he or she doesn’t even use it based on its behavior."

Use TACC all the time, see all its flaws on speed up and braking on its own, this topic. Owners posting about the erratic behavior of the cruise control are one of the most common owner complaints.

teslamazing | 16. februar 2020

Why do u use it still is the real question. Livin on edge aye ?

FISHEV | 16. februar 2020

"Why do u use it still is the real question."

Why you make false comments is still the real question. The OP is not me and is seeing the problem.

Pg3ibew | 16. februar 2020

I have a few silly questions. Does your house only have 110v service? Rare but possible.
Do you only have 1 single garage? Very possible. But then you wouldbt be asking about charging 2 cars at one time.
You are buying a 2nd 40 thousand dollar car, which means 80 grand, minimum, worth of cars. Why are you afraid to spend 2-3 grand for 2 Wall chargers and an electrician? Where I come from, we call that penny wise and dollar foolish. Or, in other words, CHEAP AS ALL FUCK.

teslamazing | 16. februar 2020

Lol bet.

Pg3ibew | 16. februar 2020

Sorry, i dont k ow how the above post got here. Meant for another post.

brscpo | 16. februar 2020

Similar thing happens to me when driving on I4 through Orlando. The Interstate is under construction and lane shifts are common.

I suspect the car believes i changed from the interstate to a surface road and adjusts accordingly.

The issue repeats in the same places and so far, no where else.

DiminishedSeventh | 16. februar 2020

@brscpo is it actually changing your set speed or just decelerating the vehicle? If the lane shift causes a sharp enough curve, TACC should decelerate to safely maneuver through the curve. Not sure if that’s happening in your case or not. Are you near an off ramp when this happens? If there is a lane shift (especially to a shoulder) plus you’re by an off ramp, the vehicle may think you’re taking the off ramp based on the GPS and slow the vehicle. Also, are you on TACC or Autosteer? Autosteer will restrict your speed when not in highways and drop you to 45 mph if it can’t determine the speed limit. TACC shouldn’t do this.

brscpo | 16. februar 2020

@DiminishedSeventh - The curves are not sharp when this happens and the lane shifts are more more than 4 or 5 lanes, on elevated roadway. It happens with TACC. It is not decelerating due to traffic ahead. I do not use autosteer in this area because of the issues that came up. When I attempted to use Navigate on autopilot, it would also get confused instructing me to turn when turns are not possible.

DiminishedSeventh | 16. februar 2020

Interesting. Is it changing your set speed (the number between the - and +) or just decelerating?

You may be right if the lane shift is so drastic, it probably thinks you’re no longer on the highway.

eandmjep | 16. februar 2020

It did that to me 2 weeks ago and I was on the freeway Cruise only in lots of construction zones where they will use Solid white lines to shift all the lanes simultaneously. Realized that the on the Map my location would suddenly put me in the middle of the off ramp. My speed would drop from 70 to 40 pretty hard. Almost got rear-ended the first time. Driver must have thought I was nuts :)

WEST TEX EV | 17. februar 2020

I have noticed a related situation but only when on TACC (lane keep active)

When on surface street speed limit 45 MPH I have dual blue lines, I go under bridge (highway overpass). Car briefly switches to AP (single blue line, tone). Then, 100 yd later goes back to TACC (dual blue, tone).

My theory is misinterpreting that I am not on highway.

Only happens with lane keep active, not just cruise....

brscpo | 17. februar 2020

@diminishedSeventh - Yes, the speed changes - the number between the - and the +.

keith | 17. februar 2020

I am surprised that the behaviour experienced by people is so disparate. My own experience is that TACC behaves as described by @DiminishedSeventh, and if I come to a section of road with a lower speed limit it is up to me to alter the target cruise speed. I do not have FSD, and mostly do not have auto-steer engaged but use TACC a lot.
@brscpo: The target speed is the one inside the blue circle I think.

DiminishedSeventh | 17. februar 2020

@west tex ev what you’re describing is Autosteer. TACC is just speed, no lane keep assist. What you’re describing (the single blue line) sounds like Navigate on Autopilot (NOA). NOA should only turn on when you’re:

1) on a highway;
2) have Autosteer engaged, and;
3) have a destination set in your nav

It sounds like it thinks you ARE on the highway from the GPS and then canceling it when it determines you are not. That’s why it only happens on Autosteer and not just with TACC.

Are you going slowly under the overpass? The amount of time near the underpass may trigger the algorithm to activate NOA. For example, if you’re stopped at a traffic light under/near an overpass.

@brscpo you’re probably right with your assessment and it thinks you’re no longer on the hghway.

@keith right on. That is the normal behavior. I think with enough details, all of these instances of variation from the normal behavior can be explained. Usually it’s either a construction zone, or some other factor that causes the GPS to think the vehicle is no longer on the same roadway it was on before. Unfortunately with computers, it’s black and white. If these conditions are met, then do this action. Until we can create computers that can think for themselves, there will always be these kinds of hiccups. And as is the case with product reviews, it’s usually the bad experiences that people post about online. You never see “I drove 90 miles with TACC activated today and nothing happened” posts.

andy | 17. februar 2020

There are very occasional changes.

The GPS database contains a lot of inaccuracies, partly due to new roads being built and speed limits being changed by the various authorities. The car also gets mixed messages where there are multiple roads running over or under each other. Speed limits also change in real-time, but that's another story as they usually drop rather than increase.

When you're driving across what was previously farmland then the car lets you set your own cruise speed with auto-steer. If the car has an incorrect database then it occasionally dislikes your audacity in reading roadsigns and tries to limit the speed where auto-steer can be used. The answer is to get the car to read roadsigns and not rely on the GPS. It'll come.

FISHEV | 17. februar 2020

"The answer is to get the car to read roadsigns and not rely on the GPS."

Different issue as even if the car can read the speed limit signs on the highway, basic adaptive cruise should not be using them, just do the set speed the driver sets, basic good adaptive cruise with no surprises.

If one then want's to activate MAP based adaptive cruise, that should be a selection vs. forcing AP people to use the problematic functionality of FSD which is where all the issues with adaptive cruise originate from the changing set speeds to auto braking, all the problem issues people report for adaptive cruise.

andy | 17. februar 2020

You lost me completely in the second paragraph I'm afraid. Maybe you're doing my thing of typing on a mobile or maybe just my lack of comprehension(?)

There's a relevance in the first - the car limits the speeds at which auto-steer can be used. If you rely on the GPS database, and the database is out by 30mph then the car will limit the use of auto steer to below the speed limit. If the car read speed signs then it would know that, potentially, the GPS database is incorrect.

andy | 17. februar 2020

..just to add. In all cases the car is erring on the side of caution. The driver always has the option of driving manually, just as we were taught to.

howard | 17. februar 2020

It most certainly changes on its own with no warning. Coming back from DIA last night I was on E470 heading northwest toward Broomfield and when I went under the I25 overpass it suddenly dropped from the set 85MPH to 75MPH. The whole stretch is 75mph unless it picked up the lower speed limit for I 25 which I passed under. I had to scroll it back up to 85.

FISHEV | 17. februar 2020

"the car limits the speeds at which auto-steer can be used."

AutoSteer is a bit different than Adaptive Cruise, this topic.

Does adaptive cruise accle, decel based on GPS road data? Yes it does.

Does adaptive cruise brake when it should not? Yes it does.

Those problems are not due to base adaptive cruise. Those problems are due to imposing Full Self Driving requirements on top of adaptive cruise.

The problems could be eliminated for base adaptive cruise by removing those FSD requirements. There would be no unwarranted changes of speed setting, no braking for overpasses and other phantom threats. Driver sets speed and car remains at set speed and follows traffic in front. Easy to do and safer than Tesla's current mixed system.

rxlawdude | 17. februar 2020

I've seen it DECREASE the TACC setpoint speed on curvy transition roads in Orange County, CA.

andy | 17. februar 2020

"AutoSteer is a bit different than Adaptive Cruise, this topic."

I tend to conflate the two within the overall Autopilot, which we also know isn't positioned as FSD and, as I understand it, is Adaptive Cruise with the extra option of engaging auto-steer if you want to. The differing behaviour with auto-steer is helpful in this context as it tells us something about what is going on with the database.

I may be getting confused with the earlier versions - only have Autopilot here as a standard part of the car.

As is typical in Internet forums, the topics meander about a bit. I've experienced the car braking in Autopilot, I've seen the displayed set speed change and not been away of touching the scroll wheel and I've had the car slow when in Autopilot with auto-steer set when the GPS speed drops - in this instance the car puts a message up to say that auto-steer is limited to a specific speed.

In normal circumstances I've not found that the car slows down for changes in GPS speed limits. Not many places I can test this though as, by definition, I have to ensure that I am at a new speed limit when I reach a sign. I'd need to be somewhere where the GPS speed limit is incorrect.

FISHEV | 17. februar 2020

"I tend to conflate the two within the overall Autopilot"

In context of speed change by adaptive cruise, AutoSteer is not relevant BUT we never know what dependencies Tesla has built into the software. It could very well be that TACC behaves differently with AutoSteer enabled, with Navigate via AP enabled, etc as happens with Lane Keeping.

None of this is documented by Tesla for some reason.

ReD eXiLe ms us | 17. februar 2020

Hmmm... Sounds a bit like 'Cop Avoidance Mode' in operation. Cool.

Big_Ed | 18. februar 2020

My car slows down in AP at 2 spots on my daily commute. One is a slow down zone where the road transitions from highway to surface. The other is where traffic from one highway merges onto another via a ramp. At both locations, I get a message saying "Autosteer limited to 5 MPH over speed limit."

When in TACC only, it does not slow down at those locations, regardless of speed.

jerrythorburn | 18. mars 2020

Three times this morning on the interstate TAAC slowed abruptly. The max speed fluctuated rapidly through multiple speeds while the slowing was occuring. It did the same thing once last week. Prior to that it has worked perfectly for the last 3 years. It seemed to occur near exits even though I was in the far left lane. One of the places was the same as last week. I am not sure why it is all the sudden occuring. I don't think I have had a recent update.

jerrythorburn | 18. mars 2020

Three times this morning on the interstate TAAC slowed abruptly. The max speed fluctuated rapidly through multiple speeds while the slowing was occuring. It did the same thing once last week. Prior to that it has worked perfectly for the last 3 years. It seemed to occur near exits even though I was in the far left lane. One of the places was the same as last week. I am not sure why it is all the sudden occuring. I don't think I have had a recent update.

gparrot | 19. mars 2020

This behaviour occurs to me too on my commute to the cottage - and it never happens in the same places. But it does occur two or three times over 464km. While driving at 115km/hr, the car decides to slow down to 100km/hr (the speed limit on the highway). On one occasion, after its slowdown, I brought the speed back to 115 and the car decided to bring it back down once again to 100. It behaved the second time I sped back up to 115 and decided it wasn’t going to win this fight. Both times I used the scroll wheel to re-adjust my speed.

LostInTx | 19. mars 2020

I've experienced the same behavior as the OP, most recently about 2 weeks ago. I was on I-10 between San Antonio and Houston. There's a stretch between Luling and Columbus where there's absolutely nothing. My speed, as indicated by the UI, suddenly dropped from 80 to 65. I'm diving in NoA mode.

This isn't about construction, overpasses, small towns, other traffic, sunspots, deep state conspiracies, change in terrain, adjacent frontage roads, construction - none of that. It's about NoA, for reasons known only to itself, decides, to markedly reduce the speed of the car.

Even before the car slows from 80 to 65, I'm able to spin the wheel and get it back up to 80. It just happens.

And let's not be so naive to think our cars won't behave in a way contrary to what's in the manual. If that were the case, we'd never receive updates that include "bug fixes".

keeper0 | 22. kan 2020

I also saw this recently and was surprised.

I only use TACC (auto-pilot is disabled). I had the speed set to 75, looked down and the set point had dropped to 70. On a 300 mile trip, it changed the set speed about four times.

I haven't take a long drive in a while due to global circumstances, so I don't know what software update messed this up, but it is definitely real.

NthMonkey | 25. kan 2020

This happened to me several times yesterday while on NAV. Cruising down the highway, clear skies, no bridges or off ramps, no speed limit changes. Car started slowing, I looked over at the screen and saw the cruising speed that was set at X was now set at X-10. This happened no less than 4 times within about a hundred miles. WTF?

And yes, I also have the random sudden slowdown from time to time also, as if the car is jamming on the breaks. Also clear roads and no idea what the car could be reacting to. Double-WTF?

NthMonkey | 25. kan 2020

By the way, this was on 2020.16.2.1, the most current update in wide release.

howard | 25. kan 2020

This has been an issue since I purchased the car 18 months ago. There are lots of Tesla fan explanations thrown out but the bottom line is Tesla has never seen it as a priority or simply can’t fix it. I would be happy with a none adaptive cruise function just to maintain speed but even that is not available. Simple software selection but no that might cast shade on the future of FSD. Joke!

EVRider | 26. kan 2020

Are those of you seeing this speed limit issue using the new auto stop on red light feature? That feature adds speed restrictions, and although it shouldn’t matter on the highway, I wonder if it’s related.

SalisburySam | 28. kan 2020

@EVRider, good point...hadn't thought of that. I too have v16.2.1, and recently upgraded HW3.0. My NoA seems to work ok but phantom braking is worse in this release, at least for me.

Unlike @LostInTexas, I do think it is map related but that's not an answer, and certainly not a solution. My thoughts agree with @howard: give me a way to turn off the TA part and be dumb-old cruise control when I want it, that is, until phantom braking is eliminated.

FISHEV | 28. kan 2020

@EVRider | May 26, 2020 Are those of you seeing this speed limit issue using the new auto stop on red light feature?"

Only have AP. I do have HW3 and it does sometimes visualize the settings on the lights. TACC still changes based on what it thinks is the posted speed limit. This can be up (merging onto a 40 mph road at 35 it will set speed at 40 instead of actual speed of 35 that driver has selected) or down, 70 mph speed limit it thinks is 50 mph.

Don't think Tesla will ever free adaptive cruise from the clutches of "Full Self Driving".

WW_spb | 28. kan 2020

Howard and Fish lil bit upset bc Tesla is destroying competition and they are stuck with best EV car available on the market.

Rhinodad | 28. kan 2020

@brscpo I have the same experience on I-4 in the construction zones in Orlando. When it happens the map seems to show that I have jumped to the adjacent surface street.

hunte001 | 29. kan 2020

Hi,
I'm a new T3 owner. Unexpected deceleration on cruise control has happened twice in the first week of driving, both times going around a "right - bending" curve at 62 mph that was very easy to do at 62. Speed limit was 55 but I'd been at 62 for a couple miles without a problem until the curve.

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