Brake Lights with Regenerative Deceleration

Brake Lights with Regenerative Deceleration

On a recent test drive, I noticed that the regenerative "braking" causes a pretty dramatic deceleration in normal mode.

I am concerned that the brake lights don't come on for this deceleration which is at least as strong as light braking action or down-shift engine braking from the perspective of other drivers.

Does anyone know if brake lights come on? Am I the only one who thinks this is worth considering? What's the best way to get this feedback to Tesla?

Thanks for your time and consideration.

- Justin

PS - My Model S just released to production. Can't wait!

JDun | 19 May, 2013

Hi justin,
Yes they do come on. You can actually see that represented in the Tesla car animation that you can view when you touch the Tesla icon. It also show when you touch the break pedal and which headlights are turned on.

njelectric | 19 May, 2013

Good luck with your new car. You will love it. Yes the brake lights come on. It is hard to know when but it is determined by an accelerometer.

justin | 19 May, 2013

Great. Thanks for the info and the tip regarding the "Tesla" status app.

- Justin

riceuguy | 19 May, 2013

Also, at night turn on the rear view camera and you will see them light up like a Christmas tree. They are very well calibrated to come on at the point in between normal engine braking slow down and hitting the brakes slow down...

markhanso | 23 July, 2013

Has anyone noticed regenerative brake lights not working ?

Have 850 miles on a 5 week old P85.

I am constantly getting tail gating drivers when I'm slowing down with regenerative braking. I know that this is an issue because I almost never have such tail gating events in my Maserati or Range Rover.

Wonder if there is an auto test / diagnostic ?

negarholger | 23 July, 2013

@Mark - hit the Tesla button it shows you the image of the car and in real time the lights.

AmpedRealtor | 23 July, 2013

@ Mark.hanson - maybe the tailgating is due more to the words "TESLA" on the back of your vehicle than the speed at which you are driving :)

ThorensP | 23 July, 2013


Those tailgaters may just be looky-loos. I still find myself pulling in behind a Model S and grinning as I try to keep up with it. The Tesla grin extends beyond the owners. Wannabe owners get it, too.

Brian H | 23 July, 2013

Touch the "T" logo on the big screen, and a live real-time image of the car appears. It will show brake lights go on and off.

pdx4s | 23 July, 2013

does the rear camera app lets you take a snap-shot of the tailgating driver ? or better video capture it... might help with road rage issues...

wife says once I get my car to place the "If you can read this you are too close, DO NOT TAILGATE" sign/sticker in the back. Rear ended accidents are probably the most frequent accidents lately for some reason, people don't pay attention/ are distracted by phones, are in a hurry etc. and then you never get the car fixed as it was before so better to avoid getting rear ended if possible.

AmpedRealtor | 23 July, 2013

Just slow down until the person goes around you and passes in huff. Then all is well again.

RZitrin1 | 23 July, 2013

I think my brake lights come on but the lights on the Tesla screen do not.

Anyone else experience this?

Brian H | 23 July, 2013


mkh1437 | 24 July, 2013

I've noticed that the brake lights seem to illuminate if you lift completely off the accelerator, but if you just back off the pedal slightly, even though regen does kick in, the brake lights don't come on. As others have said, it seems to be pretty well calibrated to illuminate the lights under conditions "equivalent to" braking, but not to the degree that it looks like you're riding the brake pedal, which was a concern of mine.

SCCRENDO | 24 July, 2013

Tried it this am. Break lights on my Tesla screen definitely come on when I start pulling my foot back from the accelerator before touching the break

Brian H | 24 July, 2013

Did the brake break?

olanmills | 24 July, 2013

@Mark, the brake lights always come on when you press the brake pedal.

Aside from that, an accelerometer is used to detect the amount of deceleration happening when you are using regenerative braking, and the brake lights will come on beyond a certain threshold.

This threshold is set such that in some scenarios, where a regular automatic transmission ICE car might have to use the brakes to slow down or maintain speed (when going downhill), and thus the brake lights would come on, in the Model S, the brake lights don't come on in these sort of gradual slowing situations.

However, I have found that they work perfectly. They come on if the amount of slowing is significant enough that other drivers need to be alerted.

I think the brake lights work perfectly as is.

carlk | 25 July, 2013

Using accelerometer to active the brake light is still different from the conventional way. It triggers the light only AFTER you have slowed down whereas brake pedal triggered light will come on when you just intend to slow down. I don't know how sensitive the setting in MS is but it's something MS drivers need to pay attention to.

Bob W | 25 July, 2013

I agree with @olanmills, it works perfectly, no changes needed here.

The Model S accelerometer triggers the brake lights milliseconds after you lift your foot off the accelerator (with Regenerative Braking set to Standard, but not when set to Low). You can see this easily on a dark empty street at night, just by looking in the rear view mirror or at the backup camera while you lift your foot completely off the accelerator. It doesn't come on when you slow down only slightly.

In a panic stop situation, the Model S is theoretically a little safer than an ICE, because it gives the driver behind you a fraction of a second more warning. The brake lights come on a bit before your foot actually reaches the brake.

Caveat: Most drivers use a single foot for both accelerator and brake. For those who drive with two feet, one on the brake and one on the accelerator, there would be no timing difference. But I think such drivers may be rear ended more often, even if they rear end others less often.

RZitrin1 | 25 July, 2013

Mine work, brakes and lights. I - not so much. Need new glasses.

stsanford | 25 July, 2013

I checked on this today... I don't get any brake light illumination from <30, but say 40-60 on at highway speeds, the brake lights to get triggered...

Loving it!

RedShift | 25 July, 2013

The accelerometer does fine for turning on the lights when you slow down. I checked all the thru my commute home today.

It's as fast as conventional brake lights. Only issue I have is when regen'ing at freeway speeds. It still turns on the lights, (which I don't really mind, its safer this way) but might feel odd to following motorist coz the car is really still going relatively fast, but brake lights are on...Just curious about that , that's all.

jjaeger | 25 July, 2013

@carlk is right - all MS drivers shall now and forever forward, use their left foot to hit the break pedal oh so little to just have the brake light come on and then - and only then - shall they let off the accelerator pedal with their right foot,thereby engaging the MS regen. Under this more sage and sane scenario - the brake light will come on - before - the car begins to de-accelerate, therefore giving ample warning to all cars in the nearby vicinity that the MS is going to being slowing down.

carlk - thank you ever so much for raising this thread and for highlighting this significant deficiency of the MS. Only with such judicious and thorough attention to detail will the MS community be truly safe.

All - I plan to report in tomorrow at this time with my new experiences now that I understand the danger and harm that I used to be in and now will be avoiding with this newfound insight.

thomas2V | 25 July, 2013

All I can tell you guys is that I am so used to using just the regen for braking that when I Have max charge I feel like I am without brakes !

Brian H | 25 July, 2013

Changing speed is what you need to warn trailing drivers about.

RedShift | 25 July, 2013


Yes, that feeling gave me some nervous jitters recently before embarking on a long journey. No, the car did not warn me with a message or the dashed yellow line the first time. Second time, there was a dashed yellow line warning me that regen capacity was reduced.

carlk | 26 July, 2013

@jjaeger You're welcome. I appreciate that someone who can pick up this fundamental, and maybe significant, issue instead of outright rejection of the idea like I got from many forum members in another thread. I guess any suggestions that a Tesla design is less than perfect is not acceptable here.

MS drivers need to aware that your brake light will only light up when you have ALREADY slowed down. The reaction time of the light will likely not be instantaneous otherwise it will be on all the time, which is also not acceptable. The gap between you and the car behind you will be significantly reduced when driver of that car first see your brake light. Be always alert of car behind you when you use one pedal control but I would just use the coast mode for now until there is more understanding of this issue.

DTsea | 26 July, 2013

No carlk. It comes on as soon as deceleration begins. You slow down after. With an ICE car the moment you touch the brake pedal the light comes on and the deceleration is not instant either. It's the same.

I say again... first you decelerate... then you are going slower. The light comes on as you START to slow down, not AFTER you have slowed down.

After 7600 miles in my Model S I have noticed zero issues with cars riding up on my rear- and I do pay attention.

I have however noticed that I have fewer instances of gap closing in FRONT of me since the regen starts deceleration before I touch the brake pedal.

I also notice I am more patient in city traffic because the car slows down more easily when I lift my foot (no foot switching).

Apparently, you didnt catch jjaeger was teasing/kidding you.

I respect your passion... but the way the Model S operates is SO MUCH BETTER than conventional cars you can only realize it by driving it.

carlk | 26 July, 2013

@DTsea I say this because I do remember someone said on this forum he feels cars behind him are closer to him when he's driving the MS. No, the accelerator only senses the "change of speed" which means it can act only when you have slowed down. Not to mention you can't set it too sensitive or else it will be on all the time.

Either way I'm not driving your MS so you make your own driving decisions. I'm happier if that is not a problem for you or any other MS driver.

tobi_ger | 26 July, 2013

The "change of speed" is certainly detected within fractions of a second, i.e. within only a few meters of driving distance, so that the brake lights will light up not after, but during deceleration.

Iowa92x | 26 July, 2013

Panties in a bind over nothing...I've always driven manual transmission cars, where engine braking can be significant when letting off the throttle. No brake light with engine braking and never an accident or even close to an incident.

hnashif | 26 July, 2013

When I first got the car I noticed that more drivers are tailgating me, until I realized that since I never drove a hatchback before, the distance from the rear window is closer to the rear end of the can than all sedans I drove.

EcLectric | 26 July, 2013

@carlk and @jjaeger,

You are so right. The roads are littered with all the wrecked cars caused by people letting out the clutches of their manual transmission cars to slow down, and everyone behind them crashing into them because the break lights didn't come on.

Why don't you two switch to the BMW forum and raise the alarm about this dangerous problem. You will probably save countless lives with your 'discovery'. Don't let the sarcasm hit you in the ass on your way out.

Bob W | 26 July, 2013

@carlk, I don't think you understood, so let me try again. With Regen=Standard, your brake will lights come on before your foot even reaches the brake. It happens that fast. As I said, you can see the effect for yourself on a dark road, at night, by looking in the rear view mirror.

I have not had any unusual problems with tailgaters. The Model S appropriately warns drivers behind you that you are slowing down well before a conventional ICE would.

nhurst | 26 July, 2013

carlk - My goodness but your physics are different from mine. Acceleration is sensed virtually instantly. Slowing down takes time - after acceleration (deceleration) begins. That is, disregarding Coriolis and hysteresis forces.

ian | 26 July, 2013

I just have to add that I'm glad I'm not the only one to catch jjaeger's tongue in cheek poke at carlk. Funny stuff!

Oh yeah, I have to add that there is NOTHING more annoying to me than when someone drives with two feet and rests their left foot on the brake pedal keeping their brake lights lit ALL THE TIME. How worthless is that? I can't tell when you're slowing down!

I don't have an S yet but on my test drive the regen was much stronger than I anticipated but can see how great it would be to drive with.


carlk | 26 July, 2013

@Iowa92x I've been driving nothing but manual (except when I drive my wife's car) in the last 30 years. Engine brake is pretty weak unless you're in low gear.

@nhurst Funny that you mentioned physics. I happen to have a Ph.D. in physics. I'm not kidding! I guess I'll just have to find it out myself when I test drive it or even when I get the car. As a stock holder and potential owner (99% sure) I'm happy if it's not an issue but I still need to find it out myself.

@goneskiian I did sense he was not sincere. For which I say to him #$@% you.

EcLectric | 26 July, 2013


My apologies for missing the obvious sarcasm.

jjaeger | 26 July, 2013

@carlk - you work in Milpitas and I live there - so let's get together and start planning how to expand the support for the GO TM FART system. I've received numerous IMs over on TMC and a few direct emails here (as I've posted my email previously) so am sure that this is the beginning of something really big. Elon has his Hyperloop as his next project - and I'll let you take half the credit for FART :-)