Scary Braking Revisitied

[EVOldtimer]

I am starting a new thread because the other one got pretty off topic.

http://www.mynissanleaf.com/viewtopic.php?f=30&t=4765

Some Nissan Leafs have a dangerous braking condition, and as of October 2013, Nissan is clueless about how to fix it. There are two very disturbing symptoms that my 2012 exhibits in panic stopping or hard braking situations. The first symptom is that the braking system will continue stop brake the car for a significant time after you have released the brake pedal. The second symptom is that the car will come to a complete stop all by itself long after you have released the brake. It is important to separate these two as distinct symptoms because it is too easy for someone to make excuses about why a car's ABS might keep going for a few seconds. You cannot excuse a car stopping all by itself--dead stop in the middle of a roadway.

Please limit your comments here in this thread to the condition where the Leafs come to a full stop, all by themselves.

My story: EV driver since the nineties, I have built a bunch of EV conversions, automotive technician, skilled driver, aircraft pilot, EV advocate/activist. I love my Leaf and am really impressed overall with how well Nissan did it, but I am apprehensive about driving mine now because of the crazy brakes. I am breaking down and posting here because Nissan has told me that it is "expected behavior" from the car. Wow...

My first episode happened at 30MPH when an animal ran in front of me and I hit the brakes very hard. A moment later it appeared to the side and out of the path of the car so I released the brakes. By now right front tire was screeching and smoking and the ABS was chattering. I glanced in the rear view mirror and happily noted no cars behind me, because a few moments later we were now sitting slightly angled in the lane, and fully stopped. I released the brake while still going at least 25 MPH but yet the car decided to stop in the middle of the road. That was very disturbing.

I took it in to Nissan. They agreed there was a problem and re-calibrated the pedal stroke sensor. I took it out for several test drives and it seemed to be fixed. (At least the ABS was no longer letting any wheels lock and skid and screech and smoke.) The brakes still stayed applied long after the pedal was released, but I could not get it to come to a complete stop, unexpectedly. Then, one day, coming around a curve at 30 MPH I came face to face with some dumbaxe in a SUV, in my lane. I jabbed the brakes, she dropped her phone and swerved back into her lane and flashed past me. Now, with my foot off off the brake, my Leaf ground to a dead stop. This time I DID have cars behind me but they were not tailgating and saw my brake lights in time. I can only imagine how puzzled they were about why I was sitting still in the middle of the road...

Nissan has refused to take any more action, based solely on their one/first look at the car. I suggested that they send a regional tech rep to drive with me, but they closed the case instead. They say that since it is an intermittent problem that the technician was unable to duplicate, they cannot do anything about it. I am assessing my options, but wanted to get a discussion going. I am going to do a report to NHTSA, so that should be added to the list there soon. From searching the internet, it is clear that my car is not the only one doing this.


Speculation and opinion:
All of the Leafs I have driven have this excessive lag in the brake release. It is hard to say how many will "dead stop" by themselves since it is so hard to recreate that specific symptom. The Leaf uses a type of braking system very different from traditional brakes. These may be 'teething issues' with implementing the powered master cylinder. I think this may be a matter for the engineers to go back and redo the software. The first thing they need to do is get rid of the condition where the brakes keep applying long after brake release. If this is part of an active braking system, it sucks and it is dangerous. I see big lawsuits on the horizon and a loss of respect for one of the pioneers of EVs. As drivers, when we start or stop a control input, we expect the controlled function to respond, whether it is brake or throttle. I don't want any car to anticipate what I am thinking, they just aren't smart enough for that yet. Hey how about a throttle that really doesn't believe you when you lift your foot off it? Is that next?

Also, the brake lights stay on while the car is unexpectedly braking. One of my coworkers speculated that the brake pedal spring might be too weak and not returning the pedal quickly or hard enough. I might try adding a spring to see what it does, but feel the clock is ticking. I am not comfortable with this car. Good driving skills are only good for so much if the car does not act as expected. I can retrain myself to "get into the throttle" instead of coasting after a brake slam, but it is not natural, and is a little difficult to do if you really did do a panic stop, because you body is slightly out of position from the deceleration forces.

Has this happened to you?

 

[goaliepride]

I'm new and this hasn't happened to me. Why I'm posting is that I've work tech support and currently do programming verification, and want to help you.

How I think you're most likely to get this fixed is the following: Get it to be reproducible. Find some lonely stretch of road/parking lot and figure it out. If you need to slam on them going 35, do so, if not try 30, 25, 20, 40, etc.. If it's not slamming on the brake, try easing into it. Maybe it's only when the brakes are warm, or maybe only when cold, try both. Do whatever you need to do to make this something you can show them every time.

If you can get it to be consistent, then you can get their attention. You would understandably be wanting to link it to your past case, don't (if you can help it). Your last case was/is one of intermittancy, so trying to re-open that closed case isn't as helpful. This new case you'll open next, well, that's a reproducible problem (we can demonstrate that!) that may or not be related (we're not trying to link the issue).

That's how to help, and get the attention of, any tech support personnel. Good luck on getting it to be reproducible.

 

[kubel]

Long story short, when humans encounter panic stop scenarios, they have a tendency to not fully depress the brake.

Many cars (including the LEAF) are equipped with Emergency Brake Assist, which basically tries to detect when a driver is panic stopping (based on how quickly the brake pedal is pressed), and will increase pressure for you. A false positive from this system can result in the car stopping rather abruptly when you rapidly press the brake.

It's an annoying feature and I wish there was an easy way to defeat it, because I would. I've experienced two false positives, and I'm really glad there wasn't someone tailgating me both times it happened.

 

[gbarry42]

I would like to see a formula for reproducing this (although I don't know if I can bring myself to stomp the pedal at speed). I have had to get on the brakes a few times but never have had this happen. I'd like to know if this feature is lurking in my car. And you of course would like to know how common this problem is.

 

[ttweed]

The first symptom is that the braking system will continue stop brake the car for a significant time after you have released the brake pedal. The second symptom is that the car will come to a complete stop all by itself long after you have released the brake.

I have experienced the first "symptom" exactly once, which as kubel has expained, is a function of the Emergency Brake Assist programming. It can be avoided completely by not "jabbing" the brakes, but applying pressure smoothly and progressively, first shifting weight onto the front tires with a gentle application of the brakes to increase their traction before applying full braking power. This is actually the best and fastest way to stop any car, especially one without ABS, since a shock loading of the front tires will break their traction, causing them to skid instead of grip, actually increasing your braking distance. Most people who haven't practiced threshold braking in non-ABS cars are not able to accomplish this discipline in a panic situation, thus the popularity of ABS in modern cars. In low grip conditions like rain, snow, or ice, it is even more difficult to modulate the brake pedal for maximum stopping efficiency, so manufacturers have substituted a computer system for driver skill, which has resulted in much greater highway safety overall. Unfortunately, people are not that familiar with the "feel" of the ABS pulsing through the pedal and sometimes do not apply enough pressure or lift off the pedal when it kicks in--thus the further "advancement" of EBA programming has been adopted widely.

I have never experienced the second symptom you describe of the car stopping itself after releasing the brakes. In my one experience of "panic" braking, coming over the crest of a hill at 65 mph to find stopped traffic in front of me, I was too abrupt on the brake pedal and the ABS kicked in, then continued for 2-3 seconds even after I lifted off the pedal, but ceased when I pressed again on the accelerator pedal at about 35 mph. Did you ever apply the "go" pedal while the car was continuing to come to a full stop?

Your description of a front tire locking and "smoking" is a little troubling as well, because a properly functioning ABS system should prevent lockup--that's its job.

TT

 

[mkjayakumar]

is this anyway related to these three topics on 'Grabby brakes':

http://www.mynissanleaf.com/viewtopic.php?f=8&t=6086&hilit=grabby" onclick="window.open(this.href);return false;
http://www.mynissanleaf.com/viewtopic.php?f=30&t=6580&p=145283&hilit=grabby#p145283" onclick="window.open(this.href);return false;
http://www.mynissanleaf.com/viewtopic.php?f=8&t=8305&p=183872&hilit=grabby#p183872" onclick="window.open(this.href);return false;

 

[TomT]

The one time I maximum braked I experienced exactly the same thing. As soon as I touched the accelerator again, the brakes released.

I have never experienced the second symptom you describe of the car stopping itself after releasing the brakes. In my one experience of "panic" braking, coming over the crest of a hill at 65 mph to find stopped traffic in front of me, I was too abrupt on the brake pedal and the ABS kicked in, then continued for 2-3 seconds even after I lifted off the pedal, but ceased when I pressed again on the accelerator pedal at about 35 mph. Did you ever apply the "go" pedal while the car was continuing to come to a full stop?

 

[EVOldtimer]

The grabby brakes issue was addressed by Nissan with a controller upgrade. Here is a partial descriptrion from the text of the bulletin they issued:
"
Reference: NTB12-086A

Date: October 25, 2012
2011-2012 LEAF;
BRAKE PEDAL SENSITIVE AT SPEEDS BELOW 15 MPH

This bulletin has been amended. The Title, Applied Vehicles, Applied VIN and Date, and If You Confirm sections have been revised. Please discard all previous versions.
APPLIED VEHICLES: 2011-2012 LEAF (ZE0)

APPLIED VIN AND DATE: Built before JN1AZ0CP(*)CT 023494 // June 6, 2012

IF YOU CONFIRM
^ Customer may experience some brake sensitivity at speeds below 15 mph. The customer may experience this issue while in stop-and-go traffic conditions.

And
^ No DTCs are present in the Electrically-driven Intelligent Brake Control Unit.

> If DTCs are present, refer to the specific section of the applicable Electronic Service Manual (ESM) and diagnose first.

"
and etc....

You will see that it only applies to grabby brakes, at speeds below 15 MPH.

Doubtless they launched an investigation and discovered an unexpected consequence in the software, had it rewritten, and then issued an updated program download for the controller.

My Leaf has fantastic brakes, and excellent tires (Ecopia EP422). Every car I have ever driven in Minnesota winters has had either winter or severe service (Nokian) tires. This car is my first exception because the combination of chassis and tires actually works in snow and below zero temps. My tire standards are very high and it surprised me that I was able to use the OE tires. After they recalibrated the pedal stroke sensor, the ABS is working correctly, in that there is no skidding or smoking anymore.

Now, Nissan needs to feel some heat and fix THIS Leaf brake problem, before more people get hurt.

To summarize what I know about Leaf braking problems:

2011 and 2012 grabby brakes in stop and go traffic was fixed with a program update and can be downloaded into your car (for free I'm sure) by your local dealer. If they try to charge you for it, just raise holy H*** because it is a safety update.

The second issue is that the brakes stay applied long after the driver has lifted their foot off the pedal. Some folks are making excuses for this, but it is a dangerous departure from normal control inputs, and has no place in a car controlled by a person, not an autonomous vehicle. This issue is NOT the subject of this thread!!!

The third and most dangerous braking problem the Leafs have is their ability to come to a complete, full, and unequivocal stop in the road, long after the driver has removed their foot form the pedal. That is the car stops unexpectedly. This is the subject of this thread.

In trying to recreate this symptom, I have observed that it is more likely to full stop when:
It is a real panic stop in the wild.
I attempt it for the first time. (But not necessarily.)

It is LESS likely to full stop when:
It is raining or wet.

I cannot tell any difference with gentle turns, or down hill (yaw or pitch), but it seem like these are likely factors. (The cars have pitch and yaw sensors, so they know what is going on...)

Because it has been raining here quite a bit, I have been unable to do more testing. And I totally agree that one key to getting this dealt with is to be able to replicate the symptom at will. Nissan should be doing this on their test track instead of me burning through tires.

 

[DaveEV]

I have never experienced the second symptom you describe of the car stopping itself after releasing the brakes. In my one experience of "panic" braking, coming over the crest of a hill at 65 mph to find stopped traffic in front of me, I was too abrupt on the brake pedal and the ABS kicked in, then continued for 2-3 seconds even after I lifted off the pedal, but ceased when I pressed again on the accelerator pedal at about 35 mph. Did you ever apply the "go" pedal while the car was continuing to come to a full stop?

That is key, I believe. I don't recall ever having brake-assist being actuated, but application of the accelerator should deactivate it. I do believe that for people with performance driving experience, application accelerator when you want to maintain speed or slow down less quickly is more natural.

Best thing to do - go find an abandoned road and experiment!

 

[Den]

You cannot excuse a car stopping all by itself--dead stop in the middle of a roadway.

Why not? At least it is what you SHOULD do BY LAW, at least in Europe, I don't know exactly about US, but mind says it should be same... law says: In emergency/panic situation ONLY thing you can/should do is STOPPING WITHOUT CHANGING DRIVING LINE. So by law, whatever the EMERGENCY situation is, you can't turn, accelerate or do something else (even you feel it will help). You can just stop! Otherwise you will be guilty!

So Nissan do exactly what is required by law. If it detects emergency situation in your behavior it stops the car and it is really the ONLY right behavior. If somebody dumps you from the rear after that - it is his fault - KEEP DISTANCE!

 

[TimLee]

You cannot excuse a car stopping all by itself--dead stop in the middle of a roadway.

Why not? At least it is what you SHOULD do BY LAW, at least in Europe, I don't know exactly about US, but mind says it should be same... law says: In emergency/panic situation ONLY thing you can/should do is STOPPING WITHOUT CHANGING DRIVING LINE. So by law, whatever the EMERGENCY situation is, you can't turn, accelerate or do something else (even you feel it will help). You can just stop! Otherwise you will be guilty!

So Nissan do exactly what is required by law. If it detects emergency situation in your behavior it stops the car and it is really the ONLY right behavior. If somebody dumps you from the rear after that - it is his fault - KEEP DISTANCE!

You must be kidding?
It is the driver's responsibility to avoid the accident by any safe means possible.
That includes changing lanes to avoid the impact, and even accelerating away from the possible impact.
If I had used only panic braking in the lane I'm in for my driving lifetime, I would have been involved in three accidents over my 40 years of driving that I instead managed to avoid.
If the LEAF engages complete stop on seeing panic braking, and will not release the panic braking with application of the accelerator, then that is just bad design.

 

[dm33]

Our 2013 LEAF was totaled this week in an accident. Definitely panic stop at work. Car performed wonderfully and prevented any of the four of us from having serious injuries but I wish it had stopped faster to avoid the accident. Now we're looking at replacing it with another LEAF I'm even more concerned to make sure it is safe.

What model year LEAF did this happen in?
Has anyone attempted to reproduce? Sounds easy. Maybe I'll even do it if I test drive another one. Most of the cars I've owned I've tested the ABS brakes but had never done it with the LEAF.

 

[DaveEV]

Our 2013 LEAF was totaled this week in an accident. Definitely panic stop at work. Car performed wonderfully and prevented any of the four of us from having serious injuries but I wish it had stopped faster to avoid the accident.

If you want the best stopping distance, you'll want tires sticker than the stock Ecopias. The '13 SL with the 17" Michelin tires probably stop better. I haven't been able to find any tests to confirm that, though. If getting a S or SV, you will probably want to replace the stock tires earlier with something of higher performance. The Ecopias roll great, but traction is not their strongest suit. Car reviewers have tested the 60-0 stopping distance at around 126-130 ft which could be better (that distance seems fairly typical for cars in the same class) - cars that generally stop faster have more performance oriented tires. Summer tires could easily shave 10 ft off the stopping distance if not more.

 

[braineo]

I bought turanza serenities and I'm very satisfied with grip, silence and ride. SO far 2,5000 miles on those tires. My Ecopias were replaced at 10,500 miles due to wear.

 

[TomT]

+1!

It is the driver's responsibility to avoid the accident by any safe means possible.
That includes changing lanes to avoid the impact, and even accelerating away from the possible impact.
If I had used only panic braking in the lane I'm in for my driving lifetime, I would have been involved in three accidents over my 40 years of driving that I instead managed to avoid.

 

[kubel]

So by law, whatever the EMERGENCY situation is, you can't turn, accelerate or do something else (even you feel it will help).

A child jumps into the road. Insufficient time to brake. Sufficient time to veer. What would you do? Brake simply because that's "the law"? Just a suggestion, but don't ever feel you are morally obligated to obey the commands of the ruling class simply because someone calls it "law". Europe, of all places, should have learned this lesson.

 

[mwalsh]

Got a similar one for you. Just happened. Not been able to replicate it in maybe 4-5 times doing similar since.

Doing 75mph; car behind up my arse; applied brakes while keeping foot on accelerator pedal. Car slowed some, as you might expect, but continued to slow another 5mph once I'd let off the brake pedal and pushed down harder on the accelerator pedal. Quite a strange feeling, pushing down on the throttle only to have the car continue to slow.

Obviously we're now down to 70mph, so a-hole behind me is just furious. :lol:

Trying to replicate it was, of course, without some jackass trying to mount me from behind.

 

[voganni]

Nissan must've changed something on the 2013's. I've had to make a couple panic stops due to deer running in front of me. The car stopped incredibly fast, with no drama. ABS worked fine. Brakes released immediately. Glad I was in the Leaf instead of on my Harley! :lol:

 

[EVOldtimer]

Ok, A couple of comments from the old timer:

I am glad you weren't hurt when your Leaf got totaled!
-----
Tire traction and performance is way more complicated than just putting "performance" tires on your car. It makes a huge difference where you live in the world and how the weather affects your driving. In So Cal you might want to switch the tires from the Ecopias. But, many so called performance tires suck in the rain, too. In MN the Ecopias perform well in a wide range of heat, cold, wet, and dry, so they are staying on my car. If I need to replace them, though, I will then switch to Nokian four season ties. The stopping behavior I have experienced was with a fully stock car. Since the 'full stopping' symptom seems to be related to the deceleration rate, yaw, and/or pitch, I can only guess it would be WORSENED by stickier tires.
-----
I have driven several 2012 Leafs like mine and they all continue to stop long after the brake pedal was released. I cannot comment on the 2011 or 2013 cars. If you are thinking of buying a 2013, just do a panic stop on the test drive and note whether the ABS is still chattering a second later. This is too important to allow a sales person to put you off and say you can't do it. (Didn't you see that rabbit?!!!) What about it 2011 and 2013 owners? Do your cars keep braking? I would not have bought mine if I knew it did the continued braking.

I explained the situation to a friend who is a Pro Rally driver. I sent a long email explaining how some people think the cars should do this continued braking. Here is the complete text of his email:

"Bad idea."

Those of us who drive seriously, especially in marginal traction conditions (winter is almost six months of the year here...), expect control inputs to respond to application and unapplication immediately. I agree with him that this is a "bad idea". And I suspect that it is the root of my full stopping symptom. I drive many types of cars daily for my work. I have never seen a car keep braking unless it had a problem and was in for repair.
-----
I would strongly recommend against ever stepping on the brake and throttle at the same time. How the car responds is a software issue, and I would expect that the car is likely to behave oddly and inconsistently when you do that. The software is constantly looking for malfunctions and might perceive that as such. It is just as likely to do a panic stop because it thinks the throttle has stuck! A flash of the brake lights should do the trick without slowing you down too much.
-----
And, that reminds me.... Do you know what to do if your car accelerates and you think you are NOT pressing the throttle? Lives could be saved if every driver went to a parking lot and figured out how to kill a runaway car. Practice finding the key and turning it off. If you have a "smart start" type, hold the start/stop button down. It might take an eternity, but it will really be only a couple of seconds. As a tech, I have had scores of cars run away on me . It is more common than you might think. (All of mine ended uneventfully, FWIW.) Of course, most of the time the driver is on the throttle INSTEAD of the brake. But they better have their seat belt on when the engine turns off and they are standing on the brake...

 

[TimLee]

And, that reminds me.... Do you know what to do if your car accelerates and you think you are NOT pressing the throttle? Lives could be saved if every driver went to a parking lot and figured out how to kill a runaway car. Practice finding the key and turning it off. If you have a "smart start" type, hold the start/stop button down. It might take an eternity, but it will really be only a couple of seconds. As a tech, I have had scores of cars run away on me . It is more common than you might think. (All of mine ended uneventfully, FWIW.) Of course, most of the time the driver is on the throttle INSTEAD of the brake. But they better have their seat belt on when the engine turns off and they are standing on the brake...

As someone who experienced one instance of a runaway vehicle (non anchored floor mat slid and hung under the accelerator), EVOldtimer has some good advice.
That day I did manage to control the vehicle while standing on the brake with both feet, and was seconds away from turning it off when I discovered the hung floor mat.
Fortunately in the LEAF three quick succession pushes of the "smart start" button will kill it. You also can stop the acceleration by shifting into reverse which will put it in neutral.
But in some "smart start" vehices, like the Toyota the family died in and similar to the one that Toyota paid a $3M settlement plus undisclosed punitive damages in a settlement yesterday in Oklahoma, you must hold the "smart start" button pushed in for a very long time while you panic brake and steer.