Brakes slamming on in cruise control

[Bobbins]

My commute's 45 miles each way, 5 days a week. In my previous car (select a suitable high end executive barge and insert here) I used to select cruise, sit in the inside lane and chill to an audiobook or some suitable music. Had the M3 for three months and for the first 6 weeks I tried all ways to get the autopilot to work for me, but no, just a stressful nightmare and a battle between me and technology.

I've slowly worked out the issues, sudden braking under bridges is usually because it picks up the speed limit on the road above and brakes to bring the speed down, it also hits the brakes if it decides the vehicle that's moving out of the lane you're moving into hasn't quite cleared the lane, virtually to the point where it's shadow is still there but nothing else.

Then at 6 weeks I cracked it ... I don't use it now, never. Too stressful trying to get the system to behave in a normal way. I can only assume that when Elon gives us FSD he'll also be sending some nice Tesla branded travel sickness pills, we'll need them.

 

[AndrewGR]

I hadn’t heard the theory that braking under bridges was because of the speed limit on the crossing road but it sounds very plausible. Has anyone noticed whether the speed limit on the display changes at the same time? It should if this is the reason.

 

[Drew57]

I hadn’t heard the theory that braking under bridges was because of the speed limit on the crossing road but it sounds very plausible. Has anyone noticed whether the speed limit on the display changes at the same time? It should if this is the reason.

Whoa! .....applying logic to why a Tesla does something!!

 

[pgkevet]

All Teslas are linked via the central computer. Every time someone hits the brakes in Beach Buggy a random Tesla somewhere slams them on too....

 

[rEV gadget]

I hadn’t heard the theory that braking under bridges was because of the speed limit on the crossing road but it sounds very plausible. Has anyone noticed whether the speed limit on the display changes at the same time? It should if this is the reason.

This is what it seemed to do to me the other day on the M61. As I crossed under a junction roundabout the speed on the screen dropped to 40 and the car braked. Wife was not impressed!

 

[Wol747]

One that I thought I had sussed out was when it braked suddenly as we drove up and over a hill - more a rise - which had an overpass right at the summit. It seemed as if the car saw the overpass as something in the road, since it was pointing up due to the slope at that point.

But then it hasn't done it again there. Just other places!

 

[Wol747]

One that I thought I had sussed out was when it braked suddenly as we drove up and over a hill - more a rise - which had an overpass right at the summit. It seemed as if the car saw the overpass as something in the road, since it was pointing up due to the slope at that point.

But then it hasn't done it again there. Just other places!

 

[NorfolkMustard]

This is what it seemed to do to me the other day on the M61. As I crossed under a junction roundabout the speed on the screen dropped to 40 and the car braked. Wife was not impressed!

The blue Max speed in the middle of the screen or the red speed limit on the right of it?

 

[Pablosammy]

I hadn’t heard the theory that braking under bridges was because of the speed limit on the crossing road but it sounds very plausible. Has anyone noticed whether the speed limit on the display changes at the same time? It should if this is the reason.

I did notice that my speed limiter dropped a bit on some of the braking occasions (set at 70, and then noticed it had dropped to 65 or so after the braking). I initially put it down to personal error, but a momentary change of speed limit might have that effect too I suppose. Definitely a plausible theory.

 

[snowywhite]

I got my M3 LR 2 weeks back and it has done this braking even when not required and has caused at least 2 instances where the cars behind have honked like I was a noob (which is not unfair) - my mate with FSD says it's the same for his car

 

[rEV gadget]

The blue Max speed in the middle of the screen or the red speed limit on the right of it?

Definitely the blue max speed that I noticed. Not sure about the other I was too busy cancelling it to keep motorway speed up. I wonder if it was because the road above was still technically part of the motorway - M65 crossing over M61 - but slower due to roundabout. It didn't seem to do it with other roads crossing the motorway.

 

[Silicon Desert]

I've just finished my first long motorway drive after finally venturing out of rural Suffolk.

I was hoping autopilot would make the journey nice and painless, but it kept me on my toes and made me look like a bit of a tool. Multiple times while in adaptive cruise (non-FSD model 3) the car would slam the brakes on without warning and no message on the screen. The common denominator for all occurrences seemed to be bridges over the motorway - they seemed to spook the car into hitting the brakes. It was very dull, dark and wet these last couple of days, so I'm wondering if the cameras were struggling.

Is this a common phenomenon? Or should I have a whinge to Tesla? It doesn't seem very safe, and for the time being I'm glad I didn't pay for FSD. It still seems rather glitchy.

I'm a long way from Suffolk, but it is not a common problem for me. I recently took a 4800 mile trip across the USA and back. Most of that on interstate highways; yes hundreds of overpasses. I never had this happen even once and I was on FSD most of the time. Now having said that, I used to have this problem on firmware versions of a few months ago, but not recently. Sometimes, it would brake on the shadow of a high overpass pipeline . I'm just glad it has stopped doing that on our car for whatever reason. Guessing due to a recent firmware update.

 

[MrBadger]

Presumably you have a nav update too? Ours is over a year old.

 

[ItsNotAboutTheMoney]

I'm a long way from Suffolk, but it is not a common problem for me. I recently took a 4800 mile trip across the USA and back. Most of that on interstate highways; yes hundreds of overpasses. I never had this happen even once and I was on FSD most of the time. Now having said that, I used to have this problem on firmware versions of a few months ago, but not recently. Sometimes, it would brake on the shadow of a high overpass pipeline . I'm just glad it has stopped doing that on our car for whatever reason. Guessing due to a recent firmware update.

There's a phantom braking cycle.

Firmware updates: Reports come thick and fast
Firmware update: reports quieten down

Unfortunately, Tesla doesn't have dumb cruise control available for the period on a bad update.

 

[Silicon Desert]

There's a phantom braking cycle.

Firmware updates: Reports come thick and fast
Firmware update: reports quieten down

Unfortunately, Tesla doesn't have dumb cruise control available for the period on a bad update.

Thanks, yes aware of phantom braking. Isn't that what OP is talking about? Maybe I am not understanding something.

 

[Jez_GB]

Had a little jaunt up the M1 today - North Notts to Leeds SC, it was the worst journey I’ve had for phantom breaking. Also car was meandering between the lane markers more than I have previously noticed, it wasn’t ping- ponging as some have experienced in the past, but it wasn’t great, the car was also keeping uncomfortably left - turned it all off in the end

Was a bit disgruntled with the car, but the loaner is a 5 year old S P85D..... missing the 3! I shall be gruntled to get it back

 

[Cnixon]

...

Unfortunately, Tesla doesn't have dumb cruise control available for the period on a bad update.

What would happen if the front windscreen camera was covered leaving just the radar operational?

 

[Dilly]

What would happen if the front windscreen camera was covered leaving just the radar operational?

I expect it would pull over, brake and phone home

 

[pdk42]

Given that most of our experiences are all pretty negative, I find it astonishing in the US that (a) they let you leave it engaged without any steering input, and (b) that some drivers trust it enough to completely ignore the road. I recall one poor guy being killed when AP got confused over an exit ramp causing the car to crash into a concrete crash bollard. Apparently, he was playing a game on his phone at the time. His family commented afterwards that he'd previously mentioned the car doing odd things at that junction. I mean...

 

[Drew57]

...I find it astonishing in the US that... they let you leave it engaged without any steering input.

Not my experience.

When my Daughter first got a Model X (Oregon) end 2018, the requirement for steering input on FSD/Autopilot was minimal but it still needed to detect some contact.The most recent time I've driven it was March this year & the wheel now requires slight input every minute or so (ie far less than the 15 sec in Europe).

Most of the time FSD seems to work much better than in the UK (she had the HW3 upgrade last month & drove California-Nevada-Idaho without any phantom braking during long stretches between SCs). Probably mapping related?