Unexpected acceleration while braking

[gabeincal]

I know most of you will doubt what I'm going to share here.

I was in San Jose, getting off the freeway, taking a left light turn from the offramp and then was doing about 25-30mph when I got to an intersection that had stopped traffic on the opposite side (cruise and autopilot was off). I had a green light, so crossed the intersection and while crossing, started to brake. Had a couple uneven potholes in the intersection (it was a little rough to cross) and while braking, I felt a short bit of acceleration like I left the cruise on or something similar, except my right foot was firmly (and only) on the brake pedal. Based on what I know about cars and specifically Tesla's, the car should ignore any acceleration signal as the brake overrides that signal. Yet, while braking, I would swear that the car accelerated by about 5mph in a very short period of time (probably 0.x seconds). It felt like somebody punched the accelerator for me. I know.. I know.. You'll all be pointing at me for having my (US size 7 ) foot half on the 'gas' pedal, or blame me for being drunk, but I know it happened.. After that intersection, I put my left foot on the brake and tried to accelerate with my right foot - which of course the car ignored as I was braking. Called the Palo Alto service center and told them the exact timestamp to look into logs and anything else they can find. Obviously, i'm not too worried that the car will suddenly kill me, but it is not a nice feeling and something somewhere is buggy... Anyone else experienced something like this?

 

[McRat]

On many cars with regen and ABS, the ABS take precedent. So when a wheel RPM drops rapidly without the others dropping, it shuts off the regen and kicks into ABS mode. What it feels like, is the car jumping forward, when all it really is, is the regen shutting off to allow the ABS to have full control of traction.

I have no idea if that's what happened, but you could experiment with a couple sheets of smooth cardboard or thick plastic. Drive towards them so one wheel will hit the sheets, then apply brakes firmly right before you hit them with your front tire.

 

[gabeincal]

On many cars with regen and ABS, the ABS take precedent. So when a wheel RPM drops rapidly without the others dropping, it shuts off the regen and kicks into ABS mode. What it feels like, is the car jumping forward, when all it really is, is the regen shutting off to allow the ABS to have full control of traction.

I have no idea if that's what happened, but you could experiment with a couple sheets of smooth cardboard or thick plastic. Drive towards them so one wheel will hit the sheets, then apply brakes firmly right before you hit them with your front tire.

And that is what I was thinking is that ABS stopped the regen. This is possible, although (and quite frankly it's hard to remember the exact things happening at the time) I felt acceleration, rather the lack of deceleration. And also, I felt no ABS 'play' on the brake pedal and no ABS or stability light came on on the dash (afaik)... But the potholes really might have something to do with what I experienced.

 

[SMAlset]

On many cars with regen and ABS, the ABS take precedent. So when a wheel RPM drops rapidly without the others dropping, it shuts off the regen and kicks into ABS mode. What it feels like, is the car jumping forward, when all it really is, is the regen shutting off to allow the ABS to have full control of traction.

I have no idea if that's what happened, but you could experiment with a couple sheets of smooth cardboard or thick plastic. Drive towards them so one wheel will hit the sheets, then apply brakes firmly right before you hit them with your front tire.

That sounds like a logical explanation if one of the wheels went over/in the pothole.

And gabeincal, believe you! Glad you called in and gave them your time to check. Curious what they come back with. Hey see you upgraded to the 75 and your car is rear wheel not AWD.

 

[Logan5]

For what it's worth I had a similar experience a few days ago. I was not coming off a highway, just a on a local road with AP off. I noticed I went over some uneven road when this incident occurred.

It may very well be what McRat described. The feeling of acceleration was abrupt but very brief. It makes sense that the ABS was taking over from the regen braking. Speed was about 20 MPH at the time.

 

[McRat]

You will often feel that 'kick' when you go over a wet manhole cover while decelerating, or train tracks at an angle, or 2 of your tires are in the middle of the lane where the oil/gravel normally exists. Wet leaves can do it too.

EDIT: I do not know if this is what happened, only that it is commonly reported. You should still get the car checked out just in case.

 

[azred]

I know the OP made a point of saying his foot was only on one pedal, but I can never recall hitting both pedals with my right foot until driving a 2013 S loaner -- and it happened three times before I realized why I was accelerating instead of stopping. Luckily I didn't hit anything.

 

[Az_Rael]

And that is what I was thinking is that ABS stopped the regen. This is possible, although (and quite frankly it's hard to remember the exact things happening at the time) I felt acceleration, rather the lack of deceleration. And also, I felt no ABS 'play' on the brake pedal and no ABS or stability light came on on the dash (afaik)... But the potholes really might have something to do with what I experienced.

I haven't experienced this in my Tesla, but in my Volt I had it happen a couple of times and it really feels like you are jetting forward when regen kicks off. Big potholes used to be sufficient loss of traction to make my Volt disable regen.

 

[SarahsDad]

The other possibility, which has happened to me, is that cruise control was accidentally re-engaged (I've hit that instead of the turn signal before). Then uneven pavement or driving through puddles will cause the car to slow, triggering a sudden surge of acceleration in order to maintain speed. Of course, hitting the brake pedal should disengage cruise control so I can't say that's what happened here...

 

[K-MTG]

Maybe Tesla will start placing pedal dashcams.

 

[JohnnyCakes]

It was you.

 

[mal_tsla]

I don't think Tesla ABS comes through the brake pedal much, if at all, since the car can apply / modulate brakes without moving the pedal.

 

[NikeWings]

Maybe Tesla will start placing pedal dashcams.

Or sensors

 

[ChadS]

I had the same thing happen to me...about 11 years ago in a Prius. And about 6 years ago in my Roadster. PriusChat has several reports, and the consensus is usually McRat's explanation. It usually happens when there is something slippery (pothole, manhole cover, painted stripes in the rain) and the driver is braking.

It really FEELS like the car is accelerating, because you are decelerating like normal and expecting to continue, and the deceleration stops abruptly and (key) unexpectedly. Many people swear the car accelerated, and I might have said that too at the time.

I have also seen occasional reports of the same thing in LEAF, Volt and i3 forums.

 

[Skipdd]

I had the same thing happen and I posted about it (think it was ~6 months ago.) Like you, I called it into Tesla and gave them the time of occurrence. They confirmed it was ABS. Definitely freaked me out.

 

[gabeincal]

Thank you all for your confirmation! Whilst I have several track days and 7 years of motorcycling behind me (therefore I can safely tell when something is slipping) this is the first vehicle I owned that has regen! Sounds fair that regen dropping suddenly can feel like acceleration and I'll take that as an explanation! Thanks again!

 

[gabeincal]

It was you.

How pleasant.

 

[gabeincal]

Maybe Tesla will start placing pedal dashcams.

Maybe they will! And in this case that'd prove that nothing was touching the accelerator pedal! Even if something was, it wouldn't affect the braking. Please read before you comment so wisely.

 

[smartypnz]

Same as in a standard transmission ICE.... when decelerating via downshift with your foot lightly on the brake - then you push in the clutch which gives a mild feeling of accelerating. But actually, you're just suddenly not slowing as much.

 

[McRat]

Thank you all for your confirmation! Whilst I have several track days and 7 years of motorcycling behind me (therefore I can safely tell when something is slipping) this is the first vehicle I owned that has regen! Sounds fair that regen dropping suddenly can feel like acceleration and I'll take that as an explanation! Thanks again!

I also have track time in some pretty powerful cars and still enjoy it, with or without ABS or Stability Controls.
The first time I felt the regen shut off during braking, I thought the car lunged forward. A few years later, I still remember what it felt like the first time.