Another Sudden Acceleration

[Omnomynous]

At the risk of outing myself as delusional, I just joined the sudden acceleration club. Never quite believed the stories, but I'm not so sure now.

So I had a few incidents recently, nothing major and no accidents, but startling. Had the last one today. What happens is that the car lurches forward as I start to brake after coasting to a light in traffic. Happened in the rain a few times and I thought maybe I hit a slick patch or something, but today it was dry and it happened again. Each time just after coasting right as I ease into the brake. Sped up for just an instant, but I stopped it each time by screaming and braking harder. And I am certain that my foot was on the brake the whole time or I have already lost my marbles and you can stop reading now.

Have an appointment scheduled to give the mechanic a chuckle, but I also have a theory under my tinfoil hat. I think this might be to do with the regerative brake. I suspect that while coasting on regen, once in a blue moon, the brake pedal somehow disengages the regen before the brakes kick in, so after decelerating on regen, the car tries to jump back to that sweet spot where it coasts like an ICE car. It definitely speeds *up* before the scream braking, like its assuming the accelerator must be pressed to have disengaged both brakes.

So I punch the brake harder and it works, I never assume I on the wrong pedal. But I also want to believe that outside of AP, nothing should make it accelerate but the accelerator, so that leaves me with an issue with the regen/brake transition or a very selective kind of psychosis.

Don't know if or how this relates to other reports, but I am hoping to get it settled soon. Can't imagine not driving my car. I am obligated to profess my love for family, but that S is the best thing that isn't married or related to me.

 

[aesculus]

Had the last one today. What happens is that the car lurches forward as I start to brake after coasting to a light in traffic.

Just curious: Do you have creep mode turned on?

 

[Omnomynous]

I do. Think that's throwing it off? I've had creep on since I got the car in 2017.

 

[krsgio]

What was your state of charge? Could it be possible it feels like acceleration but really its reduced regen?

 

[Omnomynous]

No, I always have at least 120 by the time I get back home. And its happening as I start to brake, not when I'm releasing it. But its a similar weird sensation, just more jarring.

 

[Tam]

...What happens is that the car lurches forward as I start to brake after coasting to a light in traffic...

The action of applying a brake pedal results in the car lurches forward?

We need a car log to see which pedal was pressed that results in the car lurch forward.

I do. Think that's throwing it off? I've had creep on since I got the car in 2017.

The problem of creep is when you take off your foot from all pedals, the car still coasts at a very good speed.

Without creep, and you do the same action of taking all feet off all pedals, the car would pull you back because of the regen action.

That's why I advocate for Tesla to adopt Nissan one-pedal driving: Lifting both feet up would result in a complete halt even while the car is on its way in the middle of the steep hill (up to approximately a 30-percent steepness grade).

 

[Twiglett]

No comment

 

[appleguru]

Most likely your car is loosing regenerative braking temporarily while slowing down. This feels like “acceleration” but isn’t; is actually just a noticeable decrease in deceleration. (That is, the car is still slowing down, just less because of the loss of regenerative braking).

The brakes will always work, just press them harder.

So, to me, the question is why your losing regen. The traction control system will disable regenerative for example if it detects slipping of a wheel while braking (I believe to make ABS more effective and to prevent a further loss of traction). So if your car hits a pothole, uneven road surface (think those metal construction covers), sand, wet spot, etc... that can definitely cause what you describe.

 

[Omnomynous]

We need a car log to see which pedal was pressed that results in the car lurch forward

Agreed. I contacted Tesla to ask them to research it before my appt. My memory is clear, but I want to see what it shows, especially the delay between acceleration and deceleration because as I recall reacting, there should be no gap on the timeline to indicate a foot switching pedals.

 

[Ames]

This happened to me and initially I thought there was something wrong with the car...

What may be happening here is that your technique for braking is to keep your heel in the same place and rotate the front of your foot towards the brake. Because the two pedals are close together, you could be inadvertently pressing both pedals together as you increase braking force. Because the brake pedal is more forward than the accelerator you won't notice this until you press harder. As your foot covers both pedals it feels like the car suddenly accelerates. As a safety measure, all Teslas will reduce/cut the throttle (and beep) when both pedals are pressed but not immediately, and this can be very disconcerting while braking and approaching stationary traffic.

 

[Omnomynous]

Most likely your car is loosing regenerative braking temporarily while slowing down.

That's interesting. Its an odd pattern in that only does it occasionally, but maybe it is failing in a way that leaves a gap before the brakes are applied. It feels like a 1 second roller coaster, tho. I really do scream, and I am not afraid of speed.

 

[Omnomynous]

@Ames, yeah my feet are too skinny. Plus I usually drive barefoot, and my foot cant reach both pedals at once. But I want to see how it responds with both pedals pressed, never tried it. Might be informative.

 

[Evoforce]

If you have cruise enabled at a lower speed but accelerate the car manually above that setting, when you let off the pedal, it will decelerate down to the preset cruise speed and then you will need to brake in order to disable the lower set cruise speed. I feels like you accelerate when this has happened.

Example: Say you were traveling in a speed zone of 25 mph and you had set cruise. Then the speed zone went up to 35 mph but you accelerated to the new speed using the pedal. Then a stop sign appears and you let off the accelerator pedal and the car will regen brake to 25 mph but will resume on cruise control at 25 mph until the brake pedal is applied thereby disabling cruise function. At this point the car will regen to near stop and brakes will need to be reapplied on creep mode setting.

 

[mvotb]

When I hit washboard in the road it does that, stops regen I think.

 

[TB205gti]

Try asking if wk will look at your logs - that will tell if there is an issue or not.

 

[wooter]

The issue with logs is that your car doesn't keep logs indefinitely. Next time you experience this, you should call Tesla Support (the number on the 'about' screen where your car VIN is located) and have them save the most recent logs for analysis by your service center.

Oh, and you shouldn't drive barefoot. In emergencies, you risk retracting your foot from the brake pedal because it hurts to push so hard, right at the moment you need to brake the hardest to avoid a collision.

 

[croman]

Definitely I think it's Regen based. We get accustomed to it and when it cuts out, for whatever reason, it feels like acceleration. Could cut out for any of the reasons mentioned in this thread.

 

[Enginerd]

Can you get an accelerometer app for your phone and record some data? Graphs are much more compelling than words. It would also help to calibrate (1) what the car is actually doing vs. (2) how it feels, which are not always as well correlated as one would think.

 

[zoeconner]

This happened to me a week ago. I wish I did a bug report. I do not have creep on. I pulled into my garage and put in park. Remind you if you open door it puts it in park automatically. When i got out the car started to roll forward. I looked at my wife and both kind of freaked out.

 

[Dangerous Fish]

Most likely your car is loosing regenerative braking temporarily while slowing down. This feels like “acceleration” but isn’t; is actually just a noticeable decrease in deceleration. (That is, the car is still slowing down, just less because of the loss of regenerative braking).

The brakes will always work, just press them harder.

So, to me, the question is why your losing regen. The traction control system will disable regenerative for example if it detects slipping of a wheel while braking (I believe to make ABS more effective and to prevent a further loss of traction). So if your car hits a pothole, uneven road surface (think those metal construction covers), sand, wet spot, etc... that can definitely cause what you describe.

100% agree with all of this and would add that this can happen in any car with ABS when it encounters a sudden patch of gravel, oil etc. The feeling the driver has is that the car is increasing its speed, but it's just not decreasing at the original rate or the ABS is locking/unlocking the brakes rapidly.