Life threatening brake and B mode failure

[silverleaph]

The pedal was not stiff but super soft as if I'd suddenly lost all brake fluid and then suddenly it was firm again (gratefully!). In traditional cars if there is a loss of fluid or air in the system, you can usually sense it before total failure and can pump the pedal. This was so sudden and unexpected I didn't think to pump the pedal or go for the emergency brake.

Your description of different braking behavior sounds disconcerting although I hadn't noticed it myself. Then again the car was only three weeks old and was mostly driven by my wife.

I was really loving the car, but now have lost confidence in it. I expect the dealer will not find a fault and return it to me. I will then be forever wondering when it will happen again.

 

[DNAinaGoodWay]

There's a switch to the left of the steering wheel that you can shut off the ABS with.

 

[DNAinaGoodWay]

I expect the dealer will not find a fault and return it to me. I will then be forever wondering when it will happen again.

Be sure to check the 12V.

 

[LeftieBiker]

There's a switch to the left of the steering wheel that you can shut off the ABS with.

That shuts off the traction control, not the ABS, IIRC.

 

[RegGuheert]

When you pressed the brakes and nothing happened, are you sure the pedal actually travelled to the floor, or, is it possible that the pedal simply felt super stiff (almost like pressing against metal) and provided very little braking effect?

This question is always asked in these threads. I can tell you that it definitely goes to the floor when the ultracapacitor is at a low voltage. I know this because my dealership had to rent me another vehicle when they reprogrammed the brakes on my LEAF. This was the first time the technician had ever done that service and he missed the procedure to recharge the ultracapacitor. They would not give me the car back because of "no brakes". I asked them what that meant and they explained that the pedal simply goes straight to the floor. After sitting at the dealership over the weekend, the ultracapacitor had recharged itself and the car has been perfectly fine since (that was a year and a half ago).

Since that time, I have been much more vigilant about ensuring that the 12V battery is maintained at a very high SOC. Unfortunately, the LEAF tends to keep it at about 60% with our driving habits.

 

[DNAinaGoodWay]

There's a switch to the left of the steering wheel that you can shut off the ABS with.

That shuts off the traction control, not the ABS, IIRC.

Oh yeah. Duh! Sorry.

 

[DNAinaGoodWay]

When you pressed the brakes and nothing happened, are you sure the pedal actually travelled to the floor, or, is it possible that the pedal simply felt super stiff (almost like pressing against metal) and provided very little braking effect?

This question is always asked in these threads. I can tell you that it definitely goes to the floor when the ultracapacitor is at a low voltage. I know this because my dealership had to rent me another vehicle when they reprogrammed the brakes on my LEAF. This was the first time the technician had ever done that service and he missed the procedure to recharge the ultracapacitor. They would not give me the car back because of "no brakes". I asked them what that meant and they explained that the pedal simply goes straight to the floor. After sitting at the dealership over the weekend, the ultracapacitor had recharged itself and the car has been perfectly fine since (that was a year and a half ago).

Since that time, I have been much more vigilant about ensuring that the 12V battery is maintained at a very high SOC. Unfortunately, the LEAF tends to keep it at about 60% with our driving habits.

Thanks for that. Was unaware of this ultracapacitor. Sounds like a major flaw. I'll be sure to watch my 12V more closely now.

 

[RegGuheert]

Thanks for that. Was unaware of this ultracapacitor. Sounds like a major flaw. I'll be sure to watch my 12V more closely now.

While the MY2011 and MY2012 LEAFs definitely had an ultracapacitor for the braking system, I should state it is not at all clear whether it exists in MY2013 and later LEAFs.

For reference, here is a brief discussion between Ingineer (Phil) and me regarding the whereabouts of the ultracapacitor in the 2013:

Thanks for all the pics, Phil!

I have a couple of questions about the 2013 LEAF:

- What happened to the ultracapacitor? I thought it was required to hold up the 12V long enough to provide assist for braking. Did anyone spot it?

They have redesigned the braking system, it looks to have a hydraulic accumulator now, so it may not need the ultracapacitor. It could also be moved somewhere else instead, and they wouldn't let me stat taking the car apart.

-Phil

But regardless of whether the energy storage function has been moved from an ultracapacitor to a hydraulic accumulator, the incident my dealer had with the ultracapacitor demonstrates that the LEAF's braking system can relieve pedal pressure with a drop in the voltage of the 12V system.

Like others on this thread, I suspect that either the OP's battery voltage is low or there is a bad connection in the 12V wiring that is causing the voltage to the braking controller to drop.

 

[DNAinaGoodWay]

Thanks again. Don't know how I missed these other threads, will search for them.

In the OP, after losing brakes for less than 2 seconds, function is restored and he could safely stop.

Would that be consistent with an accumulator, an UC, or both? Or maybe a bad connection?

 

[silverleaph]

Car is back from the dealer. They found nothing wrong. Battery and all connections good (I haven't checked them myself yet).

So the mystery and my doubts about the reliability of the car remain.

 

[LeftieBiker]

Try reproducing the event, by hitting the brakes while going over various kinds of bumps, on wet roads, etc. You know where it happened, so the first order of business should be to try to determine if it's the road surface or transient traction conditions interacting with the ABS, or an intermittent issue with the car's braking system. I'd look into it even if I were sure the pedal had hit the floor.

 

[acmtix]

I crashed my leaf in the snow in Leicestershire in the UK on the 26th of December 2014. I was going about 15 miles an hour and slightly down hill, round a corner. I slammed on my brakes and this caused the car to continue straight onwards into a lamp post, rather than turning round the corner. The brakes did not respond well at all, the weight of the vehicle caused it to gain momentum and the vehicle came to a stop perched on top of half a lamp post. The wheels just span and the tow truck I called also got stuck in the snow, so mountain rescue were called.

I claimed on my insurance and the insurance company, Admiral were particularly useless. It cost a grand total of £3600 to repair.

The week after the accident damage had been repaired I checked my Leaf in for the recall on the steering column bolt that supposedly works loose at slow speeds.

http://i1.wp.com/www.w-o-r-l-d.org.uk/wp-content/uploads/2015/02/wpid-20141226_205941.jpg" onclick="window.open(this.href);return false;

So with the dodgy bolt and the weird unreliable braking I decided to buy myself a second car for winter days.

@acmtix

 

[mjblazin]

What is mountain rescue in Leicestershire? Wikipedia says the highest point is 912 feet, a spot designated as a Marilyn, a term I have not yet heard. At work I enjoy learning tidbits of local knowledge from global teammates. I suspect mountain rescue might be different from same thing in Colorado or Wyoming in the U.S.,i.e., Sly Stallone climbing up a sheer cliff in an ice storm chased by mercenaries.

 

[desiv]

I crashed my leaf in the snow in Leicestershire in the UK on the 26th of December 2014. I was going about 15 miles an hour and slightly down hill, round a corner. I slammed on my brakes and this caused the car to continue straight onwards into a lamp post, rather than turning round the corner. The brakes did not respond well at all,

To be fair, this doesn't sound like a brake issue.
You could have the best brakes in the world, car still slides in that situation..
Different tires or some type of all-wheel drive maybe (although even AWD might not help if you hit the brakes like that in slippery/icy conditions..). Lighter car, maybe..

Even then, slippery roads and hitting the brakes hard.. Expect to slide..

desiv

 

[epirali]

I crashed my leaf in the snow in Leicestershire in the UK on the 26th of December 2014. I was going about 15 miles an hour and slightly down hill, round a corner. I slammed on my brakes and this caused the car to continue straight onwards into a lamp post, rather than turning round the corner. The brakes did not respond well at all, the weight of the vehicle caused it to gain momentum and the vehicle came to a stop perched on top of half a lamp post. The wheels just span and the tow truck I called also got stuck in the snow, so mountain rescue were called.

I claimed on my insurance and the insurance company, Admiral were particularly useless. It cost a grand total of £3600 to repair.

The week after the accident damage had been repaired I checked my Leaf in for the recall on the steering column bolt that supposedly works loose at slow speeds.

http://i1.wp.com/www.w-o-r-l-d.org.uk/wp-content/uploads/2015/02/wpid-20141226_205941.jpg" onclick="window.open(this.href);return false;

So with the dodgy bolt and the weird unreliable braking I decided to buy myself a second car for winter days.

@acmtix

Wow sorry to hear. I had no issues driving the leaf in non frozen snow, handled like a very good front wheel drive car and all the weight really helped. I even could climb my very steep driveway (500 feet) with snow. Only times it failed was in icy conditions. And from the pictures it looks like it was kind of icy?

In those conditions I'll only drive AWD (Audi).

 

[acmtix]

It felt like the car lurched and didn't brake quite as well as it should have done.

Its quite hilly, not really a mountain, more of a volcano but we still have mountain rescue just in case...
https://en.wikipedia.org/wiki/Bardon_Hill

It was very icy and the surface had a rough road covering to prevent skids in icy conditions. It didn't work in my case. Teaches you to pay attention. Worst part of it is, that my insurance took over a month to repair the vehicle and they charged £3,600 to replace the front bumper and provide a rental car for the time the car was off the road.

 

[taloyd]

Whenever I hear people bring up 4WD in stories about braking in friction-compromised conditions, I have to chime in...

The only thing that stops a car, any car, whatsoever, on earth - are the 4 tires. Not the engine, not the suspension, not the marque. A 4WD car, FWD, AWD, German, Japanese, and American car all have 4 tires. If those are inappropriate for road conditions, then there's the potential for danger.

Suspension, engine location, whether or not it's a Subaru, steering input, throttle input - all of this ONLY affects dynamic weight distribution of the car - how much of the 100% of total weight is divided between the FR, FL, RR, and RL tires.

A FWD Nissan Leaf with the same tires as a Subaru (low boxer engine for a low CG) will have much the same friction potential, (though Subaru have far better suspension).

If the same tires were on any other car that weighs similarly I'm sure the same thing would have happened. ABS works surprisingly well in utilizing the available friction. If there isn't any available friction - the car will slide.

Only bringing this up because it reminds me of a friend who was driving to a snowy mountain, and said "I don't need to put on chains - I have 4WD". I quickly pointed out they have the same 4 tires as they do in the summer, and the tires don't really care if the car has 4WD or not. 4WD helps if one is going to crash because of the gas pedal. Tires help if one is going to crash because of the brake pedal.

Just my $0.02.

-Tal

 

[miscrms]

FWIW, according to the service manuals both the 2013 and 2014 Leaf still have the backup power supply unit for the brake controller. Its supposed to be located behind the finish panel on the lefthand side of the luggage compartment.

Temporary loss of either hydraulic pressure or 12V power (overall or to any individual controller) should cause a whole bunch of DTCs to be logged along with freeze frame data.

I'm really wondering if this isn't just "normal" operation of the ABS/VDC system since there isn't any log of malfunction? I know the Prius would freak people out sometimes when the ABS/TC system would kick in during braking. I believe the unsettling feeling came from regen being discontinued due to the slip detected while hydraulic pressure was also being reduced at the same time to avoid sliding. People would describe it as the vehicle "lurching forward" or even accelerating (from feeling of suddenly reduced deceleration). I suppose this effect could be even more dramatic on the Leaf in B mode as there is potentially a lot more regenerative braking force being used? This might even be a reason not to routinely use B mode for normal braking. I wonder what happens if you are braking using only B mode pedal off regen (no brake pressure applied) and the ABS/VDC detects slip?

As others have mentioned there is still a direct hydraulic path from the pedal to the calipers, but with a complete brake system electrical failure (which I've simulated by disconnecting both the IBU and ABS controllers) the pedal position will feel very low and then very stiff. This might make someone think it had suddenly dropped to the floor, when it hasn't really. But again this would require a loss of electrical power that should certainly throw DTCs.

Its also good to remember that the parking brake can be operated as an emergency brake while moving as someone else mentioned. This is cable operated (though also requires 12V power) but is independent of hydraulic pressure.

It seems like all single system failure modes should be covered.
Loss of 12V power - hydraulic w/ power assist from backup
Loss of 12V power and backup - hydraulic brakes w/o power assist (low pedal position, requires hard press)
Loss of 1 hydraulic circuit - hydraulic brakes on second circuit
Loss of both hydraulic circuits - cable operated emergency / parking brake
Loss of both hydraulic circuits and 12V power - hopefully there's a big soft snowbank nearby