Losing all regen braking during a bumpy stop

So recently I experienced the issue of losing all regen braking while coming to a stop, forcing me to really step hard on the brake pedal as I wasn't expecting any failure. Since I was worried about coming to a stop, I didn't pay attention to my nav screen to see if that's what really happened. While there was no accident, I could definitely see this type of issue causing some minor accidents.

Scenario: I was coming to a stop from 45mph (only pushing the brake pedal just far enough to slow down with max regen), and about 100' from the red light, I lost all regen braking as I drove over a small but noticeable bump (road connects to a bridge in this spot). Braking performance was exactly the same as when you first start driving your 100% charged LEAF, but in this case, my battery was ~ 60%.

I haven't been able to replicate this scenario, but another member mentioned a similar issue in another thread, so I'm starting to wonder if there is a real issue, and was some weird case of operator error. Decided to start this thread as I didn't want to hijack anyone elses thread.

User FairwoodRed also posted a response in that other thread, which adds an interesting perspective:

Your braking trouble actually seems reasonable. The Leaf uses an electronic brake force controller for the majority of its braking. The pedal is mostly just to indicate how much braking the EBC should deliver, not to actually create hydraulic pressure.

If your bump was strong enough to shake the brake pedal, then the sensor could have registered an invalid reading and the EBC could have disabled itself. A whole lot of speculation here. Others have reported similar situations where the EBC seems to have shut off and they had to use a lot of force on the brake pedal to stop. The good news is that normal braking was restored by either fully releasing the pedal, or by powering the car off and back on.

I recommend that you take your car into the dealer for a complementary safety inspection (we are talking about the braking system here). The least that will happen is that Nissan will get one more notch in the complaint column for “braking issues” and if they get enough, they put more money into improvements for future cars.

If you don’t want to go to the dealer, then consider calling 877-NO GAS EV or 877-664-2738. That is the number for EV sales and support. They will be happy to listen to your concerns and open a ticket for tracking. As with many call centers, you probably won’t get any serious help from them, but if there’s help to be had, they can start you down the right path.

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If anyone else has experienced this, please do post.

The Leaf's ABS is particularly sensitive and aggressive and that is what caused your experience. The tires lost some traction as you went over the bumps while decelerating, and the ABS intercepted this as the wheel skidding, which in turn caused it to reduce deceleration (or braking, if you will). I've had the same thing happen to me a few times...

lion said:

So recently I experienced the issue of losing all regen braking while coming to a stop, forcing me to really step hard on the brake pedal as I wasn't expecting any failure. Since I was worried about coming to a stop, I didn't pay attention to my nav screen to see if that's what really happened. While there was no accident, I could definitely see this type of issue causing some minor accidents.

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wow, the bump wasn't that big (just the typical seem between a bridge and a road), and I'm guessing I was doing around 30mph by the time this happened, so I'm really surprised about this, but the explanation makes sense as well.

Now I have to explain this to the wife, without making her think the car isn't safe.

Indeed, "something" happens when going over a bump. But the braking computers are supposed to be smarter than that. If they switch from regenerative braking to friction, they should do it seamlessly. In the real world, I do notice when this happens, but not in a manner I would call unsafe. Anything more dramatic than this would bear investigating. Most of the stuff on the car is digital, with sensor feedback. But friction brakes are physical, and analog, so there might actually be an adjustment to balance the two.

The same is true for the ABS. It may "let go" momentarily, but it had better give us our brakes back real quick or there will be trouble. The Prius had an issue like this, and it generated vast volumes of postings on the priuschat site (I'm sure cwerdna will be along shortly ) Toyota ultimately issued a firmware fix for the problem, but there was a lot more angst about it than actual problem. I observed this on our Prius and again, it was perceptible but not dangerous.

Just to be clear, I've described what's considered normal. Your description, if accurate, seems to go way outside the bounds of normal, and should be looked at.

[Note 1] There was a place or two in my normal commute that this would happen in my LEAF. But I was never able to "catch it in the act" on the nav's power/regen display.

[Note 2] I have a T-shirt that says, "Toyota: Once you drive one, you can't stop". I have to explain the joke to everyone, especially these days, because everyone has forgotten (short attention span of the media and the public).

Yep, I've experienced it on nothing more than expansion strips at relatively slow speeds, exactly what you described. There is one on the downhill off-ramp on my way to work that I can replicate the scenario on every time if I wish... I've learned to take pressure off the brake momentarily when traveling over it... Frankly, the Leaf's ABS algorithm is not very sophisticated compared to many other vehicles... Blending regen with friction brakes no doubt has something to do with it...

lion said:

wow, the bump wasn't that big (just the typical seem between a bridge and a road), and I'm guessing I was doing around 30mph by the time this happened, so I'm really surprised about this, but the explanation makes sense as well.

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gbarry42 said:

Indeed, "something" happens when going over a bump. But the braking computers are supposed to be smarter than that. If they switch from regenerative braking to friction, they should do it seamlessly. In the real world, I do notice when this happens, but not in a manner I would call unsafe. Anything more dramatic than this would bear investigating.

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Wet weather can mean that the physical brakes take a bit of time to dry off and start working. Prius (2005) does this as well. in the Prius, breaking with regen down to 8 mph, then the regen turns off and the brakes are supposed to take over. Can take a second, and you get the scary feeling that the brakes failed for that second.

Leaf can do the same thing. Braking with regen, hit a bump with wet brakes and there is a second when it feels like the brakes just failed. Doesn't seem to happen if you are braking hard enough to trigger the friction brakes before you hit the bump, or on the rare days when things aren't wet. This is near Seattle, rain happens.

I have felt the same effect in my wife's hybrid Lexus (RX400h) when slowing sharply over a bump. It's not just a Leaf thing.

Regen also seems sensitive to pedal pressure and whether it's increasing,decreasing, and at what rate. I can get all 4 bubbles to light on a certain downhill if I gently and gradually apply the brakes and then hold the level, but maybe only 1 or 2 bubbles if I apply the brakes differently -- for example if I apply a more abrupt braking and then back off. As a bump can momentarily change the brake "pedal pressure", that could change the regen profile.

Ok this seems to be happening more often now, very disappointing for sure. Now that I'm used to it, I can deal with it, but I do consider this dangerous if you have never experienced this before. I'm an experienced and very safe driver, so I was able to deal with it, but new drivers need to be warned or I can see this becoming another Toyota scenario.

Yes, I noticed this in my Leaf before and I can replicate it fairly consistently.

I too have experienced this lack of re-gen while braking.
I have 24,000 miles on the car, the battery was at 40% SOC and was the first drive on the day and has repeated for may days.
Does anyone have a real answer for this issue?

lion said:

So recently I experienced the issue of losing all regen braking while coming to a stop, forcing me to really step hard on the brake pedal as I wasn't expecting any failure.

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TomT said:

The Leaf's ABS is particularly sensitive and aggressive and that is what caused your experience. The tires lost some traction as you went over the bumps while decelerating, and the ABS intercepted this as the wheel skidding, which in turn caused it to reduce deceleration (or braking, if you will).

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In 18,000 miles, 33 months of driving a 2011 LEAF I have also encountered this braking behaviour eight to ten times.
I think TomT is correct that the anti-lock braking system is a bit sensitive and aggressive.
Usually has happened when one of the two front driven tires encountered a bump, or pothole, or change in surface such as metal plate, manhole cover, railroad crossing.
I have kind of learned to anticipate it.

Only really bad instance was when traffic was coming to an abrupt halt and I was already braking very hard. Very disturbing when you are closing in fast on stopping vehicle and the braking system decides to stop braking for 0.1 or 0.2 seconds and the vehicle moves 2 or 3 feet towards the rapidly slowing vehicle with NO braking occurring. Even though no loss of traction skidding occurred.

I'm not aware of Nissan having taken any action to correct this. They did a software change to help the brake grabbiness, but that was pretty ineffective. They need to do a lot of root cause analysis and testing and try to improve the LEAF braking, both this quirky ABS brief non-braking issue and the grabbiness.

Scenario:

Car in front of you panic stops. You have enough space and time to brake without losing traction, but there's a bump in the road. ABS kicks in and you lose out on a second of braking, and you rear end the car in front of you as a result.


Another Scenario:

There's snow/ice on the road. Car in front of you panic stops. What would have been no problem for me to gently bring the car to a stop before crashing without ABS, becomes "GrrCLKGrrCLKGrrCLC--CRASH!!!" in the LEAF with ABS.


On some cars, the ABS is almost perfectly tuned- but on this car, the ABS is a safety concern for me. I really don't care about loss of regen, I just don't like loss of braking. It's not a good feeling knowing your car can stop but won't because of some 'feature'. Same goes for emergency brake assist- car stops when you don't want it to.

I have a similar issue and also an easy solution for my problem, shift it to ECO. I live on a hill and at the end of the down hill road, there's a big turn. If I only use "D" and brake, I will lost regen brake at the turn. When I switched to "ECO", the regen brake constantly engaged even at the turn. Originally, I thought that was caused by the traction control. This has solved my issue and I have not try to disable the traction control to see if this is caused by ABS or the traction control. However this will not address if you are on the high way and using "D".

[Updated]
I further tested it for the last couple days, I've seen regen down from 4/5 to 3 for a second or two and then back to 4 when I'm at the turn, regardless of the "traction control" on or off. It seems that "my" problem is not related to the traction control. However I did not press the brake hard enough to cause the wheel lock up, so don't know if my problem can be caused by the ABS either. Maybe the bumps on at the turn or outside wheel lost contact with the surface does kick in the ABS.

This happens to me ALL the time, even in ECO. But rarely is it a major issue, it's mostly just one of the LEAF's many little annoyances.

So while I am mostly 'used' to this 'feature', I had a really close call again, and couldn't stop in time for a yellow light (one I anticipated, so I already started slowing down while still green) because of a manhole cover I wasn't familiar with. I was only doing 35MPH (40MPH zone), and lost so much braking power that I had to engage the brakes as hard as one would during an emergency stop in an ICE vehicle.

I'm absolutely fed up with this, and I'm ready to file a complaint with the NTHSA as I've never felt so unsafe before (and I've driven vehicles with failing rear brakes before). I guess I need to find time to get the dealer to check out the car again, but as usual, I'm sure they won't notice the problem.

None of my other/previous vehicles (including my Toyota Prius Plug-in) have ever malfunctioned like this.

Has anyone talked to their dealer/LEAF support about this yet?

lion said:

So while I am mostly 'used' to this 'feature', I had a really close call again, and couldn't stop in time for a yellow light (one I anticipated, so I already started slowing down while still green) because of a manhole cover I wasn't familiar with. I was only doing 35MPH (40MPH zone), and lost so much braking power that I had to engage the brakes as hard as one would during an emergency stop in an ICE vehicle.

I'm absolutely fed up with this, and I'm ready to file a complaint with the NTHSA as I've never felt so unsafe before (and I've driven vehicles with failing rear brakes before). I guess I need to find time to get the dealer to check out the car again, but as usual, I'm sure they won't notice the problem.

None of my other/previous vehicles (including my Toyota Prius Plug-in) have ever malfunctioned like this.

Has anyone talked to their dealer/LEAF support about this yet?

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What's your millage? It could be possible if you drive on bad roads a lot that your shocks are worn out and need to be replaced.

This isn't a nissan leaf thing, it's a regen braking thing. Both my Prii do it, the older one needs shocks and it does it a lot.

From my observations I would guess it happens on bumps where the car anticipates ABS might kick in and not when it actually does kick in. This is probably for safety, ie a loss of regen that causes you to give it more brake before you loose traction is better than actually losing regen when the wheels are already bouncing too much for the brakes to work. Because of this a shock that is not worn beyond it's limits yet but is close may cause this to happen more.

minispeed said:

This isn't a nissan leaf thing, it's a regen braking thing. Both my Prii do it, the older one needs shocks and it does it a lot.

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It's not even a regen braking thing, it's an ABS thing. My old Subaru did it a lot, too. Worse than my Prius.

lion said:

Now I have to explain this to the wife, without making her think the car isn't safe.

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The problem is- the car *is* unsafe.

kubel said:

The problem is- the car *is* unsafe.

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Absolutely correct.
Under certain conditions the LEAF braking is unsafe.
Overall on a risk per mile driven it may be lower risk than my 2009 Altima ICE.
But under certain conditions it is downright dangerous :!: :shock: