silverleaph
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Life threatening brake and B mode failure

Wed Jan 21, 2015 9:44 pm

My 20115 Leaf S is 3 weeks old with less than 700 miles.

I was descending an 8% grade hill in B mode with a sharp bend at the bottom. As I went to apply the brakes, the pedal went to the floor and B mode cut out. The car was now rolling down the hill and accelerating under gravity with no brakes and without B mode slowing the car. I was expecting to hit a brick wall at the bottom of the hill when suddenly, after no more than two seconds, the brakes and B mode came back on and I safely stopped. I was a bit shaken and felt very unsafe driving the car although the problem didn't recur and I haven't been able to reproduce the problem on similar grade hills. When I told my wife, she said that the day before she was going down a hill in B mode when B mode suddenly stopped working although the brakes were OK. B mode later came back on although she couldn't remember exactly when.

On reflection after the incident, it was as if the whole computer/electronics momentarily shut down and then rebooted. I didn't notice if the dash lights went off or not.

That was yesterday and today I took the car to the dealer today. After an hour or so I was introduced to a mechanic described as the only Leaf qualified mechanic they had. He said he had driven the car and there was no problem. I asked if he had driven the car in B mode downhill. Incredulously, he asked what B mode was! I asked if he had pulled the diagnostic codes and he said there was nothing recorded. I told the service manager this mechanic was not qualified to work on the car since he didn't know about B mode and they produced another mechanic who did know about B mode. We went for a test drive together but could not reproduce the problem. As the problem is intermittent, who knows when it could recur or with what consequences. The car is now with the dealer for further diagnostics.

I'll update this thread if I get anything useful from the dealer.

knightmb
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Re: Life threatening brake and B mode failure

Wed Jan 21, 2015 9:57 pm

I don't know how much reaction time you had, but remember you have an emergency brake and the main brakes can still be pumped mechanically to stop. You don't have to slam it and send your car into a skid, but you should be able to depress it enough to start the mechanical braking to get the car to stop (keep the foot on the main brake of course).

Now, that aside, I agree, very disturbing issue. Was the vehicle nearly fully charged when you went down this very steep hill? It's been known that when the vehicle has a full battery, you can't regen very much into the battery, even in B mode. This is to protect the battery for over-charging. Now, even if the regen kicks out, your mechanical brakes should still work as they are like the power brakes on any car. The only thing that would kill those is if the brake pump were to turn off. It does sound like car hit some type of shutdown mode if both Regen and Power Brakes failed.

How fast were you going down this steep hill? Was the Regen B mode helping you coast at a consistent speed or were you speeding up the entire way down the hill (before things shutdown). I actually have a long "straight" section of about a 1 mile road that goes down with this grade level near where I live. If you can give a good description of everything you remember, I might be able to perform a similar test but with no killer road curves at the bottom. :mrgreen:

Also, where in the country do you live?
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LeftieBiker
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Re: Life threatening brake and B mode failure

Wed Jan 21, 2015 10:34 pm

Going over a rough patch of road can make the ABS engage and make it feel as if the brake has stopped working, although the pedal doesn't hit the floor, IIRC. I really dislike the ABS in the Prius for that reason, and you can't easily disengage it. If you hit rough road (or a patch of ice) just as your battery got topped off, you might see that situation. Ice would also defeat the B mode even with it working properly, if there were no traction.
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silverleaph
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Leaf Number: 312502

Re: Life threatening brake and B mode failure

Thu Jan 22, 2015 2:37 am

Battery was about 70% charged when the brake and B mode failure occurred. At the time of the incident I was doing maybe 25 at the most. B mode was engaged and had been slowing the car until I hit the brakes. I use B mode a lot because I live 800 feet above sea level and B mode gets back a lot of what I lost ascending.

When B mode failed for my wife, it was close to fully charged. So are you saying that B mode is ineffective when the battery is fully charged? That doesn't seem right as the purpose as I understand is not just to recharge the battery but replicate engine braking as in a gas powered car.

I live on Maui, HI. No ice here :)

LeftieBiker
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Re: Life threatening brake and B mode failure

Thu Jan 22, 2015 2:43 am

Ok, so no ice! Water on the road might have the same effect, to some extent. And yes, while B mode does simulate engine braking, that isn't its main purpose as it is on the Prius. Its main purpose in the Leaf is to increase regeneration. Braking is secondary, and with no ICE to spin for braking, there is no way to use it if the battery can't charge.
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DNAinaGoodWay
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Re: Life threatening brake and B mode failure

Thu Jan 22, 2015 2:55 am

At 70%, you had enough regen braking, but it cut out.

And the road condition? Might ABS have come on?

Call Nissan and open a case. Possibly NTSB as well?

Hard to have any confidence in your dealer. Is there another dealer on Maui?
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cwerdna
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Re: Life threatening brake and B mode failure

Thu Jan 22, 2015 3:06 am

silverleaph wrote:So are you saying that B mode is ineffective when the battery is fully charged?
Correct. By design.

Haven't you noticed the car barely slows down in B when fully charged vs. say below 90% SoC? At high state of charge (esp. 100%), notice the almost complete lack of double circles on the regen area at the top of the dash until the battery depletes somewhat?
DNAinaGoodWay wrote: Call Nissan and open a case. Possibly NTSB as well?
NHTSA's at http://www.safercar.gov/" onclick="window.open(this.href);return false; is the right agency for those. For legitimate safety defects and not user error, file a safety complaint there as well as contacting Nissan formally, as directed in the manual. I see a section in the '14 owner's manual on page 9-15 "Technical and consumer information" about reporting safety defects that says something to this effect.

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BrockWI
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Re: Life threatening brake and B mode failure

Thu Jan 22, 2015 7:21 am

Along these lines are the brakes not physically connected to the break pedal? I fortunately haven't had this issue, but every other car I have had either had no power brakes or if it did have power brakes and the engine stalled you could pump or stand on the brake pedal and it would stop. Does this not work with the leaf? If so that seems like a MAJOR safety design flaw.
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aarond12
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Re: Life threatening brake and B mode failure

Thu Jan 22, 2015 7:50 am

The brake pedal going to the floor sounds suspiciously like another thread here. In that thread, the 12V battery was failing. This seems to have some correlation in this case, especially if the car's computer blinked out for a moment.

1. Check and re-check the battery connections.
2. Check to make sure the ground from the battery goes to the car's chassis and is secure. Even consider taking it off, cleaning it, polishing the metal with sandpaper, and re-attaching it.
3. Have the dealership thoroughly test the 12V battery.
4. Consider running LeafSpy and watching the 12V battery level.
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asemeco
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Re: Life threatening brake and B mode failure

Thu Jan 22, 2015 9:22 am

LeftieBiker wrote:Going over a rough patch of road can make the ABS engage and make it feel as if the brake has stopped working, although the pedal doesn't hit the floor, IIRC. ...
This has happened to me three times in one year. I'm lucky there wasn't a steep incline in any of the cases. It feels like a software bug.

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