My Leaf roll back and almost kill a kid!

[mkjayakumar]

In any case those Eco tree caricatures in the dash are useless and in a way stupid. It makes the owners look stupid. Take that and give some real useful information.

 

[EVDRIVER]

If the 12V battery can close the main contactor the DC/DC is on and the car has full 12V.

 

[RegGuheert]

If the 12V battery can close the main contactor the DC/DC is on and the car has full 12V.

Sure, it "can," but there are only certain circumstances where it "does." During those times when the DC/DC converter is not on, charge is being drawn from the 12V battery and its SOC is dropping.

When the DC/DC converter IS charging the 12V battery, it often does so at only 13V, which results in a very low charge rate as the SOC approaches 100%.

 

[Smidge204]

There are four hydraulic channels from the ABS controller (LEAF service manual, pages BRC-214, BRC-215), one to each caliper. I should hope that "bleeding off" of hydraulic pressure is done independently in each channel. Hydraulic pressure being relieved in one channel should not affect the other channels.

As per the diagram I linked to (and yes, that diagram is only one wheel) - there is no way for the fluid to flow back to the master cylinder except through the two lines that supply pressure to the ABS unit. If the ABS unit "bleeds of" the pressure there is nowhere for that pressure to go except into the tiny ABS pump suction reservoir. Since brake fluid is (hopefully) incompressible that's all you need to take pressure off, but even in the most extreme failure scenario the pedal will not go to the floor because there simply is nowhere for that fluid to go.

If fluid is prevented from leaving the master cylinder as soon as one wheel locks up and the ABS activates, then the three remaining calipers will not receive any additional hydraulic pressure and therefore their braking power are limited to the level it was at as soon as one wheel loses traction and the ABS comes on.

But that's not how it works, because pressure is regulated on a per-wheel basis, so there is no reason why the non-slipping wheels would not receive full force. Nowhere did I say or even imply otherwise.

The diagram shows one ABS channel for one wheel. Braking and ABS action at one wheel should be independent of the others.

Which diagram? 'cause there's lots of them. The colored one does indeed show the operation for one wheel only. This diagram, which appears near the top, shows the entire system:

Kind of self-explanatory from my point of view.

Also, that diagram shows a "closed ABS system" where a pump maintains hydraulic pressure in the affected hydraulic path. In an open system, the affected wheel simply has its pressure bled off into a reservoir. "A disadvantage of the open systems is that the brake pedal will drop during a long ABS stop as fluid flows from the brake lines."

There is no reason to believe that the LEAF uses an open system, so I fail to see what relevance that has with the issue. Using the terminology on the pages you linked, the LEAF has every indication of using a closed, non-integrated system.

I can certainly see how a software bug, or sensors malfunctioning, can cause all four channels to activate, bleeding off hydraulic pressure from each channel back into the ABS reservoir and/or back into the brake fluid reservoir, the net result being the brake pedal sinking to the floor. (I have not researched the service manual so I do not know whether the LEAF has a return path for excess hydraulic pressure back to the brake reservoir.)

I can't see that happening, because there is no place for the fluid to go. The ABS reservoir is, again, tiny and already full of fluid under normal operation. We're talking a thimble-size amount of fluid. There is no return path to the master cylinder except flowing back up the same tubing that is supplying braking pressure in the first place.
=Smidge=

 

[RegGuheert]

There is no reason to believe that the LEAF uses an open system, so I fail to see what relevance that has with the issue. Using the terminology on the pages you linked, the LEAF has every indication of using a closed, non-integrated system.

The fact still remains that the OP reported the brake pedal moved all the way to the floor. Twice. SOMETHING allowed for that to happen. The problems with the car seem to have been resolved by making an electrical change and no mechanical failures have been identified.

All of this continues to point to an electrical/electronic fault in that LEAF causing a failure in the braking system.

 

[Smidge204]

The fact still remains that the OP reported the brake pedal moved all the way to the floor. Twice. SOMETHING allowed for that to happen. The problems with the car seem to have been resolved by making an electrical change and no mechanical failures have been identified.

Which is upsetting, since it doesn't add up. Either the original account was wrong, the service manual and all other available information is wrong, or the real underlying problem still exists. According to the original story there were two incidents roughly a month apart, so it's possible it's behaving itself for now. I do sincerely hope the problem is fixed but I just can't convince myself it's solely an electronic problem.

If it really is fixed, I'd be very very interested in learning more about exactly what happened, 'cause it may just take the option of buying a LEAF off the table for me.
=Smidge=

 

[oscar]

Also for past year leading up to the issues I’ve reported in previous message. My wife was very upset why my dashboard screen doesn’t match the display clock on the navigation. Throughout the year I’ve kept adjusting the clock after it off more then 10 minutes. I had to adjust the clock a lot of time. It only takes 1.5 months for the real dashboard clock to run behind the real navigation clock. Maybe this is another indicator I can monitor in next few months. If the clock is correct on display as the navigation clock. I can then use the clock as my indicator for my 12V battery running low.

I’m not sure if anybody has his or her clock off on display and navigation clock?
This was very noticeable on my Leaf!

 

[davewill]

If the 12V battery can close the main contactor the DC/DC is on and the car has full 12V.

Having low-voltage during the boot up of the electronics could cause problems that full-voltage later doesn't correct.

 

[mwalsh]

Maybe this is another indicator I can monitor in next few months. If the clock is correct on display as the navigation clock. I can then use the clock as my indicator for my 12V battery running low.

No, that's nothing to do with the state of your 12v battery. It's just a lousy, cheap clock that doesn't keep proper time.

 

[NissanSupport]

Pick up the car this morning. Once started the Leaf mileage reading show 105 miles on display. I’ve notice the brake felt different in a way that it felt stronger not relax feel as before. I drove the car home and measure the voltage and new battery reading 12.31 volts. Anyway I will do more testing on uneven pavement testing in next few days. Hope all my problem is resolve due to low 12V battery.

Hey, Oscar. We sent you a PM earlier today following up on this. Please let us know if you received it. Thanks!

 

[surfingslovak]

Hey, Oscar. We sent you a PM earlier today following up on this. Please let us know if you received it. Thanks!

Welcome, Nissan support team, this is great to see!

 

[Ingineer]

Let me clarify a few things: You can't accurately assess the SoC and health of a lead-acid battery solely by measuring voltage. There are many factors, such the exact chemistry variation, electrolyte stratification, plate sulfation, separator type, temperature, etc.

The Leaf has a proper temperature-compensated current-monitoring multi-stage charging system. The voltage will vary depending on many factors, but should be at least 13 volts anytime the Leaf is in READY mode (Green car icon on dash lit). If it is below 11 volts when the car is off, you have a problem. My 2011 is treating the battery properly in my opinion. Sounds like Oscar had a battery with a bad cell.

Low 12v voltage can cause all kinds of problems. Yes, the Leaf should be ready for this kind of thing, but it's development is still ongoing. Since both the parking brake and park pawl mechanism are powered by 12v, a low or defective battery can indeed cause a situation where the car can roll. They seem to have fixed this on the 2013 with a return to a mechanical parking brake mechanism. (yay!)

If the 12v voltage falls while the car is in ready, you will get a red battery icon.

If you are ever going to sit in the car and use accessories, always do so in READY mode! This will prevent the 12v battery from being discharged which will greatly shorten it's life.

I have seen low voltage adversely affect ABS/Traction control systems and create unsafe race conditions. This is why Nissan included a rather expensive brake capacitor, so that if the 12v fails while you are driving, you can safely stop. If you are parked, and the car never enters ready, the brake capacitor is useless. Also, Stopping a car like the Leaf without a working brake booster is going to require enormous force on the pedal. Probably both feet.

Any Nissan tech with even minimal training should be able to dump the DTC's (Diagnostic codes) with the Consult III+ system, which should clearly point to a low 12v bus. At that point, all bets are off, as a low 12v bus can cause all kinds of other codes, both false and real. First step should always be to check the 12v system.

-Phil

 

[DTB]

I have had a few similar experiences with this brake issue, but nothing quite so dramatic. I've noticed that it seems to happen if I keep my foot on the brake pedal for several minutes with the car off and then start the car and switch to reverse without taking my foot off the brake pedal. The car will start to roll despite what would normally be sufficient pedal pressure. Pushing harder causes the pedal to drop further than normal (not all the way to the floor but the feeling is a bit disconcerting). I had to apply more pressure than I usually would in order for the car to stop rolling however a quick pump of the brake pedal and everything returned to normal.

 

[Nubo]

ok, I'm going to stop speculating.

 

[oscar]

I have had a few similar experiences with this brake issue, but nothing quite so dramatic. I've noticed that it seems to happen if I keep my foot on the brake pedal for several minutes with the car off and then start the car and switch to reverse without taking my foot off the brake pedal. The car will start to roll despite what would normally be sufficient pedal pressure. Pushing harder causes the pedal to drop further than normal (not all the way to the floor but the feeling is a bit disconcerting). I had to apply more pressure than I usually would in order for the car to stop rolling however a quick pump of the brake pedal and everything returned to normal.

yeap that's my expereince!!! I had to lift my foot off brake then slam on brake again to stop..otherwise it just a sinking feeling guys! Therefore it became a habit for me now even after 12volts battery replacement. I Start car then remove my foot from brake pedal then step on brake and Reverse. This felt safer that brake recognize my foot OFF and re-apply back ON!

I will try to keep my foot on brake at start and Reverse see if I can duplicate this issue with a new 12V replacement.

 

[Ingineer]

If the car is in Ready, the 12v is out of the equation. You shouldn't be attempting to move the car without going into ready mode.

If you haven't had the recent braking system software update, this could be why the pedal behaves funny sometimes. First, go get the update before complaining, as Nissan as fixed a lot of the issues, if not all.

Here's the TSB: Print it and take it to the dealer service dept. Tell him/her "Sometimes my brakes are indeed grabby at low speeds".

-Phil

 

[oscar]

Hey, Oscar. We sent you a PM earlier today following up on this. Please let us know if you received it. Thanks!

Welcome, Nissan support team, this is great to see!

Yes this is Great! I was surprise but this is what I wrote to them on private email.

"The experience I had on the brake rolling back was a huge concern and shocker! Especially in Reverse mode when your foot is on the brake pedal. This is the least I would expect but became a nightmare.

I guess the 12V battery was low to 10.7Volts. Maybe these cause my problems with brake and can't Start most of the time.

I hope Nissan would invest more Engineering resource into the 12Volts battery. Either bad 12volts I had but at time it let me Start. Therefore I would assume Nissan has a 12volts display on dashboard showing the 12volts level state in future!!!

What I have realized is the Leaf is 100% beauty. I would not hesitate buying Leaf again! I think most of your real world experience would be starting the car therefore the 12volts should be carefully your core focus. Many time I hated the car that it didn’t let me start. Now I found out it’s a 12volts battery. Therefore it made me more frustrated that this simple problem causing me nightmare and many time sitting in my car for 20 minutes before I could Start…that a simple knowledge of 12volts was low!!!!!!!!!!! Please add this to your dashboard display!

Also after 18 months of driving my battery is still displaying 12 bars charge! Excellent condition and I always charge 100%. Also after replacing the 12volts battery the mileage display seem to be more accurate at the start of the trip!"

 

[donald]

(At risk of digging up an old thread) I came across this while looking for info on Leaf's hill start behaviour.

Anyhow, from the outset, it sounded to me like this was ordinary brake behaviour! If you put your foot on the pedal of a vacuum boosted system and then start up the vacuum source (in ICE case, the engine, in EV case, a vac pump) then your pedal/foot will sink to the floor!?

Maybe it was just a panic reaction to something unexpected, and taking your foot off the brake pedal was not necessary at all? I think it may have been fine, and the correct thing to do, just to keep your foot on the pedal as it sank down.

This effect may have been made more obvious because the battery was flat and, whatever solenoids/pumps work, then perhaps they did not maintain the boost vacuum in the same way you had expected them to do from before.

One way or the other, the pedal could not have gone down to the floor unless there was either;
a) a seriously obvious fault/leak with the hydraulic systems,
b) there was no brake vac boost to start with, but then it pumped down on start up, or
c) the pistons in the callipers had been pushed right back away from the discs, leaving a big gap between the pads and the discs.

I can't see how 'c' would've happened, and 'a' seems unlikely if it went through the garage (and that it carried on working OK once started).

In regards the pedal locking on an irregular surface, if the transmission lock is on the front axle of a vehicle, and the parking brake is on the back, then the vehicle can become 'locked' if the vehicle is stopped on the foot brake, then the parking pawl engaged, and then the parking brake is applied.

I don't know if the parking brake on the Leaf is on the front axle or the back? If on the other axle to the parking pawl, this effect could happen. The reason is that as the chassis settles once the foot brake is released, as the vehicle settles into a new position (due to the terrain it is sitting on and the articulation of the suspension at the moment the pedal brought the vehicle to a stop ) the parking pawl will end up creating a force in one direction, and the parking brake will oppose it. If there is some interconnection between the parking and foot brake, then it may cause the foot brake to lock too.

Parking a vehicle with a parking pawl on one axle and a parking brake on the other is best done in the following sequence; that you come to a stop on the foot brake and one or other is engaged, then the foot brake must be released before the other parking aid is engaged. If you release the foot brake after engaging both parking devices on uneven ground, you may experience this effect. I would advocate that if you are engaging both (and you should, on uneven ground) that you engage neutral and the parking brake first, then release the foot brake and check it does not roll on the parking brake, and finally engage the transmission park.

 

[tombobcat]

I have the same nerve breaking problem with my LEAF, called Nissan LEAF customer support to report issue, case number 13187200.

 

[RegGuheert]

Sorry about that. Can you please measure your battery voltage and report back here?