karlboekelheide
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Leaf Number: 5142

Intermittent brake failure/problems

Tue May 20, 2014 4:37 pm

I have two problems which might be related. The first, more serious, nearly causing a low speed collision, occurred only once, two days ago. The second has been occurring for at least a year. The dealers, I've been to two, can't find any problem or error reports.

This is a 2011 Leaf that has had all the software updates. It has 57,000 miles. Never been wrecked or damaged.

The first issue is the brakes not working in a quick stop that became a panic stop. I was panicked; the car wasn't stopping. I was pulling out of a driveway at less than 10 mph. A car had stopped to let me out and was obscuring a fast moving car in the next lane out. When I saw the fast car I applied the brakes quickly. There was very little slowing of the car. I had the pedal to the floor and the car moved leisurely another 2-3 feet, at 3-5 mph, nearly being hit by the fast car. I backed up. Waved my apology and let things clear out. As soon as practical I tried several quick stops at low speed. All were what I would expect. At the extreme all 4 wheels locked and stopped the car immediately. Other, not so extreme, stops stopped very quickly just as I would expect. I just got back from the dealer who had a technician speed 3 hours testing and looking. They could find nothing. No errors. Not reproducible.

The second issue, which may be related, has been occurring for at least a year. Once in about a month, or 1 in 100 starts, the brakes don't come online correctly. The light pedal pressure doesn't work. Normally at low speed the brakes are very responsive to light pressure. Before the software fix for "grabby brakes" they were over responsive. All of that is missing. You have to press the brake harder to get any braking. Braking does occur it's just a bit sluggish. Also there is no additional regen that would normally occur when the brake is pressed. Lastly, there is click that can be felt and heard near the top of the brake press stroke. This is not a normal sound and is only present when the brakes are in this condition. The conditions will persist as long as the car is on. If the car is turned off for at least a couple minutes everything returns to normal. The clicking sound stays even with the car off for some minutes. I have taken the car to a different dealer twice and they say they can't see any problem. My guess is that the first problem is actually a manifestation of the second one. Although I have become very acute to when the second one is happening, I didn't notice the car being in that state when I nearly caused a wreck. Usually I know as soon as I stop for the first time.

Has anyone any clue or pointers to how Nissan's crazy brake by wire system works? I'm an old guy and find it really disturbing that the brake pedal does not have a physical connection to a master cylinder that squirts brake fluid in the wheel cylinders if and when the computers goof up. I'm ready to pull the dash and see what makes the clicking sound.

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TomT
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Re: Intermittent brake failure/problems

Tue May 20, 2014 4:47 pm

Actually, it is not a brake by wire system. It is, in fact, very similar to the brake system on any other vehicle except that it uses electricity rather than vacuum to power the brake booster...
karlboekelheide wrote:Has anyone any clue or pointers to how Nissan's crazy brake by wire system works? I'm an old guy and find it really disturbing that the brake pedal does not have a physical connection to a master cylinder that squirts brake fluid in the wheel cylinders if and when the computers goof up. I'm ready to pull the dash and see what makes the clicking sound.
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Re: Intermittent brake failure/problems

Tue May 20, 2014 5:20 pm

Could be brake booster or solenoid( since it is electric )issue? When was the last time you changed brake fluid?

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mwalsh
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Re: Intermittent brake failure/problems

Tue May 20, 2014 6:29 pm

I think it's the ABS. There is this one spot on the freeway during my commute home where there is a slight lip in the road surface. If I'm on the brakes when the car hits this lip, I get an immediate loss of pedal pressure that lasts for a few seconds. It's quite disconcerting, but I've come to expect it. However, it could possibly cause an accident if I was too close to the car ahead.
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Re: Intermittent brake failure/problems

Tue May 20, 2014 10:20 pm

If they dealer's been unsuccessful in repairing or trying to repro (seems you've had no luck on this), I'd contact Nissan at http://www.nissanusa.com/apps/contactus ... ntact.link" onclick="window.open(this.href);return false; (probably better by phone) and get them to officially record your issue/complaint.

If they still can't get it resolved, or after they succeed in doing so (better), I'd also file a safety complaint w/NHTSA at http://www.safercar.gov" onclick="window.open(this.href);return false;. The latter would be better as you'd have details of what they fixed.

You mentioned "At the extreme all 4 wheels locked and stopped the car immediately". That sounds abnormal. The job of ABS is to prevent wheels from locking up, so that you still have steering control during hard braking and thus have a chance of steering around the obstacle.

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karlboekelheide
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Re: Intermittent brake failure/problems

Sun May 25, 2014 1:14 pm

Thanks for the replies especially the idea of calling Nissan and filing an official report.

The extreme case where all 4 wheels lock is when I'm going only 4-5 miles an hour. There isn't enough time for the ABS to unlock. The car is stopped by then and I consider it normal.

I'd still like to see a schematic and pictures of what's actually connected to the brake pedal. I call it brake by wire because I can push the pedal to the floor fairly easily whenever the car is stopped. It was also to the floor in my panic case when the car was still slowly moving. If there were actually a piston connected to the pedal the hydraulic pressure from the brakes would prevent me from doing that. I think there is some electric function that failed in that one case.

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RegGuheert
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Re: Intermittent brake failure/problems

Sun May 25, 2014 1:42 pm

karlboekelheide wrote:I'd still like to see a schematic and pictures of what's actually connected to the brake pedal.
Here it is. Unfortunately, this is unlikely to clear up anything except to confirm that the brake pedal IS connected directly to the brakes, as was mentioned before.

My recommendation is to immediately verify the proper operation of your 12V battery. There have been reports of serious braking system malfunctions occurring when the battery voltage was low. Likely that problem was due to communications problems on one of the LEAF's CANbusses. A new 12V battery solved the problem.
RegGuheert
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Re: Intermittent brake failure/problems

Sun May 25, 2014 3:11 pm

My 2013 SV will sometimes lose some braking force at low speeds for no apparent reason. Our 2010 Prius did the same thing, but only on slick, bumpy roads. I agree that it's probably the ABS, and that Nissan probably screwed this system up as well...
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karlboekelheide
Posts: 6
Joined: Sun Jul 24, 2011 4:47 pm
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Re: Intermittent brake failure/problems

Sun May 25, 2014 4:33 pm

Reg,
Thanks for the schematic. It's not too much help other than to notice that there seems to be big white space in front of the actual piston. There seems to be a lot of confusion about whether you can floor the brake or not. I'm here to tell you that you can.

I questioned the Nissan mechanic when he did the fluid flush. At first he said, "no you can't floor the pedal because it will be mechanically applying the brakes." I said, "oh yeah, look at this" and very easily pushed the pedal to the floor. At that point he changed his tune and mumbled something that didn't make sense. Unfortunately he also said that's the way all the Leafs are and let me try another one in the shop. Indeed it was exactly like mine. 40-50 pounds of force easily pushes the pedal to the floor. After you get a couple inches down there is no increase in resistance against the foot. It just slides on down to the floor. I challenge all of you to try it. Power on or power off it doesn't make any difference. I still think (no proof only deduction and the one stop that didn't work) that if the power boost isn't activated for some reason you will have very little braking.

I'm also very disturbed by all the comments about how your brakes are screwed if your 12v battery isn't up to snuff. I don't think we should be at the mercy of so many easy to fail parts in order to have brakes. 12v batteries can fail in odd ways at odd times. What I really don't like being at the mercy of is Nissan programmers. There's way too much logic in the car. Having spent my working life time working with fail safe systems I know leaving out a direct mechanical connection to the brake pads is a real mistake.

What I don't see in any of the posts I'm looking is any communication with Nissan. Has anybody gotten an official response from them? I plan to start calling and writing next week.

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RegGuheert
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Re: Intermittent brake failure/problems

Sun May 25, 2014 6:29 pm

karlboekelheide wrote:Reg,
Thanks for the schematic. It's not too much help other than to notice that there seems to be big white space in front of the actual piston. There seems to be a lot of confusion about whether you can floor the brake or not. I'm here to tell you that you can.
I didn't say you cannot floor the pedal. In fact, that is exactly what happened to the OP in the link that I provided. What I did say is that there is a direct connection to the brakes. But I should be more clear. I meant from the master cylinder. But I do see what you mean about the white space! I certainly could be wrong, but I suspect the problem you are describing is in the ABS system and how it is implemented on the wheel cylinders. We had some discussions about that in the other thread. While we did not have details on what is implemented in the LEAF, we discussed generic systems. One possibility in that case was malfunction of the ABS system repeatedly releasing small amounts of fluid. Of course, that doesn't happen in the case you described with the power off.
karlboekelheide wrote:I'm also very disturbed by all the comments about how your brakes are screwed if your 12v battery isn't up to snuff. I don't think we should be at the mercy of so many easy to fail parts in order to have brakes. 12v batteries can fail in odd ways at odd times. What I really don't like being at the mercy of is Nissan programmers. There's way too much logic in the car. Having spent my working life time working with fail safe systems I know leaving out a direct mechanical connection to the brake pads is a real mistake.
Are you aware that there is an ultracapacitor in the back of our LEAFs which has the sole purpose of holding up the 12V to allow for sufficient braking in the case of a crash? It takes the place of the coffee can that used to hold a partial vacuum in old cars. In fact, when Nissan updated the firmware on my brakes, they could not release the car to me because the pedal went all the way to the floor. Apparently, I was the first one to get that work done at that dealership and the technician did not perform the steps which recharged the ultracapacitor. Without that capacitor charged, there was little to no braking. I don't know for sure, but I suspect that below a certain battery voltage the ultracapacitor is actively discharged to allow maintenance to be safely performed five minutes after the battery is disconnected from the car.
karlboekelheide wrote:What I don't see in any of the posts I'm looking is any communication with Nissan. Has anybody gotten an official response from them? I plan to start calling and writing next week.
I have directly communicated with Nissan on this topic, including in person and on this forum in threads that were read by them. IMO, they do not seem overly concerned.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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