Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Weird behavior of regenerative braking at higher speeds

This site may earn commission on affiliate links.
During the last week I have encountered some really weird behavior by M3 SR+ when I take my foot off the accelerator pedal at speeds above 70km/h. First, most often, the car doesn't slow down at all or very little until I press the brake pedal. Second, it sometimes even slightly accelerates in this situation. This regenerative braking is totally different from what it has been during the two months that I have owned the car.

Autopilot/cruise control is off. Regenerative braking is at "Standard".

I installed an update three weeks ago and another last week.
 
This is the weird part. The weather has been very similar here for the last month. Around 5C during the day with a few colder exceptions every now and then. There were some dots, but nothing significant. Immediately after these incidents regenerative braking worked perfectly fine at lower speeds.

The latest incident occurred after my first post. I was driving around 90km/h, took my foot of the acceleration pedal, pretty much nothing happened. Then I pressed the brake pedal lightly and the car slowed. Right after lifting my foot off the brake pedal the car accelerated slightly. It felt like if cruise control was stuck on or something. Will contact Tesla tomorrow, but probably the problem will be solved by then on this forum :D
 
I had EXACTLY the same issue above 70kmph. No dots in the powerbar, battery was like hot. I had jerky deceleration several times. I have had this issue since september. Finally I documented and timestamped an entire day with this issue and I opened a service request. Tech told me to better read how to prepare my M3 for winter driving (outise temp was 15c ) ! Since the opening the service request my gauge seems to work better and regen is collerated to the number of dots.

I think it is a cold weather software bug where M3 thinks that the battery is warm but during regen a protection kicks in and stop the regen. Then it s up to your feet brakes to slow down if there is enough space leftin front of you.
 
  • Helpful
Reactions: KenC
Thanks! I remember reading somewhere that it could be made on the website (in addition to the app). The problem reappeared during the weekend. It does not occur always when slowing down from higher speeds, but in more than half of the cases.
 
I have installed Scan my Tesla on my M3SR+, one of the reasons was to monitor regen and better understand its behaviour for high speed breaking and mountainous areas on the road. Unfortunately there is only one param on regen and it doesn’t t seem to provide any useful information. BUT I have access to my battery temperature. To get a good stable regen it has to be above 20c which is difficult during winter. Here is a map to battery temps and regen. I will update it later:

>25c full stable regen
>20c good stable regen
>14c and <18c unstable regen above 70km/h
<14c weak stable regen at all speeds
<2c no regen

And again it is VERY difficult to heat up battery from 0c to 20c, it can take 2-3hours. if it is raining, snowing : add more time ! Basically the purpose of all this study is to go further in less time during winter.
 

Attachments

  • Screenshot_20201205-105840.jpg
    Screenshot_20201205-105840.jpg
    131.5 KB · Views: 151
  • Like
  • Informative
Reactions: wws and EAV1
And again it is VERY difficult to heat up battery from 0c to 20c, it can take 2-3hours. if it is raining, snowing : add more time ! Basically the purpose of all this study is to go further in less time during winter.

It's very difficult in a model 3 that only has a rear motor because it can only make so much heat. You will also find in the RWD cars if you are blasting down the freeway it can only make so much waste heat because the motor still have to produce forward momentum. From what I've seen with the car trying to preheat the battery it actually produces heat for the battery much faster when the car is either stopped or moving slowly, not when it's going quickly down the freeway. With dual motor, this isn't really an issue because you have twice the heat generation AND even with the rear motor moving the car the front can basically be on full heat duty.
 
  • Informative
  • Like
Reactions: EAV1 and Schulmann
I've scheduled service for later this week. Interesting to find out if this can be fixed. The biggest oddity in my opinion here is that sometimes when I brake I have to "fight" against the car. In other words, if I don't brake, the car maintains speed or even slightly accelerates. Rather than just slowing down "normally", like all cars to when the foot is lifted from the pedal. This can in no circumstances be considered normal behavior.
 
I've scheduled service for later this week. Interesting to find out if this can be fixed. The biggest oddity in my opinion here is that sometimes when I brake I have to "fight" against the car. In other words, if I don't brake, the car maintains speed or even slightly accelerates. Rather than just slowing down "normally", like all cars to when the foot is lifted from the pedal. This can in no circumstances be considered normal behavior.

I’m having trouble setting the entire scene you’re describing. Is it possible to get a couple minute video of you demonstrating and narrating the problem? A visual of the horizon, speedometer and power meter would be very helpful in diagnosing your problem. See if you can capture three or four instances with varying conditions (down hill vs flat, for example). Cell phone video on YouTube is fine.
 
I have installed Scan my Tesla on my M3SR+, one of the reasons was to monitor regen and better understand its behaviour for high speed breaking and mountainous areas on the road. Unfortunately there is only one param on regen and it doesn’t t seem to provide any useful information. BUT I have access to my battery temperature. To get a good stable regen it has to be above 20c which is difficult during winter. Here is a map to battery temps and regen. I will update it later:

>25c full stable regen
>20c good stable regen
>14c and <18c unstable regen above 70km/h
<14c weak stable regen at all speeds
<2c no regen

And again it is VERY difficult to heat up battery from 0c to 20c, it can take 2-3hours. if it is raining, snowing : add more time ! Basically the purpose of all this study is to go further in less time during winter.

Regen amount will also depend on state of charge.

So if I'm reading correct, you're saying that specifically between 14C and 18C, and above 70km/h, you get weird regen behaviour? Wow. That's oddly specific. By "unstable" do you mean it's cutting in and out like on a slippery surface?

It's very difficult in a model 3 that only has a rear motor because it can only make so much heat. You will also find in the RWD cars if you are blasting down the freeway it can only make so much waste heat because the motor still have to produce forward momentum. From what I've seen with the car trying to preheat the battery it actually produces heat for the battery much faster when the car is either stopped or moving slowly, not when it's going quickly down the freeway. With dual motor, this isn't really an issue because you have twice the heat generation AND even with the rear motor moving the car the front can basically be on full heat duty.

Unless you're preconditioning the battery for Supercharger arrival, the AWD version behaves nearly identically to the RWD in cold conditions. The front motor is almost never used and is just coasting for highway travel - it still can take hours to to warm the battery by 20C, since only the rear motor is really doing work. AWD is also warming a larger battery pack, more thermal mass - it can actually take longer in theory compared to SR+.

Only when the battery is below about 0C (and not en route to a Supercharger) will the front motor be actively making heat. This isn't a super common scenario since the car doesn't allow it to rest significantly colder than that anyways

I've scheduled service for later this week. Interesting to find out if this can be fixed. The biggest oddity in my opinion here is that sometimes when I brake I have to "fight" against the car. In other words, if I don't brake, the car maintains speed or even slightly accelerates. Rather than just slowing down "normally", like all cars to when the foot is lifted from the pedal. This can in no circumstances be considered normal behavior.

Throughout this thread it really sounds like it's somehow accidentally set to cruise, which is really really weird.

There IS a minor bug with turning cruise off that impacts regen (I haven't actually tested this in a while, might be fixed). In these scenarios, are you manually turning off cruise then lifting off the pedal?

It's worth noting that in the Owner's Manual, it's sometimes expected that regen doesn't work for a while after switching to winter tires (and vice versa). It should eventually start working again though.

The other note I'd make is that letting off the accelerator without regen sometimes feels like acceleration even though it's not. I know by looking at speed and such it's not, but my darn brain absolutely swears it accelerated briefly, probably because it was expecting deceleration. This still messes me up even though I'm aware of it, it's just a hard-wired weird brain bug.

And a final note - this car coasts like no other. It's has significantly less drivetrain drag than an ICE vehicle, so it can really coast a lot further with a lot less deceleration. The "Low" regen setting is actually sort of similar to ICE vehicle "coasting" (and yet, it's actually recovering energy). This part of the car's behaviour is entirely normal.
 
Regen amount will also depend on state of charge.
Unless you're preconditioning the battery for Supercharger arrival, the AWD version behaves nearly identically to the RWD in cold conditions. The front motor is almost never used and is just coasting for highway travel - it still can take hours to to warm the battery by 20C, since only the rear motor is really doing work. AWD is also warming a larger battery pack, more thermal mass - it can actually take longer in theory compared to SR+.

Only when the battery is below about 0C (and not en route to a Supercharger) will the front motor be actively making heat. This isn't a super common scenario since the car doesn't allow it to rest significantly colder than that anyways

I was specifically speaking to routing to supercharger though which admittedly is a little off topic. You also have 2 motors warming the battery when you preheat the car which can make a big difference in preconditioning before a drive, it also however can lead to you warming the battery more than you really care for if you really just want to warm the cabin for 15 minutes. The main point I was going for is, having both a LR RWD and a LR AWD there is a big difference in how warm you will arrive at a supercharger off the freeway in cold conditions. In my experience a single motor car just can't create enough heat and push the car down the road for the battery to arrive "warm" compared to the awd.
 
I took the car to the SC. Did not cost anything, but did not fix anything either. The statement, that I cannot open anymore, said that this is a known problem and will be fixed in future updates.

The issue thus remains. Every now and then when I'm driving at higher speeds and either lift the foot of the accelerator or switch cruise control off the car slows down extremely slowly. Not really a huge problem since I can always brake, but of course nice to have everything fixed and working properly in the car.
 
  • Informative
Reactions: KenC
I took the car to the SC. Did not cost anything, but did not fix anything either. The statement, that I cannot open anymore, said that this is a known problem and will be fixed in future updates.

The issue thus remains. Every now and then when I'm driving at higher speeds and either lift the foot of the accelerator or switch cruise control off the car slows down extremely slowly. Not really a huge problem since I can always brake, but of course nice to have everything fixed and working properly in the car.

The sort of ease-in of regen after switching off cruise has been a feature for a very long time, and probably not something they'll change. This prevents turning off cruise and it suddenly slamming full regen force on. I usually compensate for this just by disengaging cruise a few seconds before I normally would want to slow down.