unexpected/unintended sudden braking- swaying and shaking

I have an unexpected braking problem with my Nissan leaf S 2014. I experienced an unintended sudden braking going downhill from 50 mpr to about 30mpr. It was scary. The car swayed and shook a lot. I thought it was going to lose balance. This happened twice again on a rather even road right after this incident. Anyone experiencing this?

Possibly it was the brake assist feature. If the system detects sudden, hard braking, the brake assist takes over and brings to car close to a stop. Apparently a lot of people in a panic stop situation initially start braking hard, but then start modulating the brake instead of keeping their foot firmly down, which contributes to rear-end collisions. Brake assist is intended to save these drivers from themselves. It's possible to "accidentally" trigger it if you move your foot quickly from the accelerator to the brake, for instance if you are surprised by something ahead of you that turns out to be inconsequential.

Thanks but I wasn't braking at all, especially considering the following two incidents happened while I was driving on the even road (after the first downhill one). There was noise, and the car swayed and shook. I felt more friction on the passenger's side.
The dealer just called and hasn't found anything yet.

If this happens with traction control turned off, then you likely have a mechanical issue. The challenge with things like this is being able to repeat the problem in a controlled way.

This sounds similar to what I felt when a bushing for the steering rack on my old car went bad. It would be fine for the most part, but then sometimes (usually when I went around a corner, but sometimes on a straighaway), I would get some bad shuddering where it was hard to keep the steering aimed properly, and it would scrub speed. The bad bushing allowed way too much play in the front wheels relative to each other.

But that was with an 11-year-old car.

I also experienced this 2 different times within a week. In my instance, I was driving on the highway with my foot on the accelerator. I did not brake at any time, but I do believe I reduced or alleviated the pressure on the accelerator as a means of coasting or slowing the vehicle in both instances. Was disconcerting enough that I switched out of the eco/B mode and just drove on D for several days. Dealer found nothing and it hasn't repeated in 3 months now.

The car was with them for about one week. I got the car back yesterday after the dealer told me that they did not find anything wrong. The assistant service manager did not quite believe my story and said it was like chasing "a ghost". But this afternoon the on-board dash showed two warning lights: one is the yellow braking warning light and the other is the VDC (vehicle dynamic control) warning light. I turned on and off the car several times and the lights are still on. I am going to bring the car back tomorrow to them again.

I finally got the car back on April 4th after it was there another week at the dealership. They installed a new G sensor. But my family lost trust of this vehicle because I almost lost control of the car going downhill three weeks ago. We are requesting a replacement to restore our confidence. The dealer is talking to their manager. So far no progress yet.

mike5466 said:

I finally got the car back on April 4th after it was there another week at the dealership. They installed a new G sensor. But my family lost trust of this vehicle because I almost lost control of the car going downhill three weeks ago. We are requesting a replacement to restore our confidence. The dealer is talking to their manager. So far no progress yet.

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Good luck. I haven't heard the problem you had described by anyone else with a LEAF.

mike5466 said:

I finally got the car back on April 4th after it was there another week at the dealership. They installed a new G sensor. But my family lost trust of this vehicle because I almost lost control of the car going downhill three weeks ago. We are requesting a replacement to restore our confidence. The dealer is talking to their manager. So far no progress yet.

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Re: the bolded part, it sounds like you experienced a safety defect. If so, seems like reporting it to NHTSA at http://www.safercar.gov/" onclick="window.open(this.href);return false; would be a good idea, if they're able to successfully repair the issue. If they can't or unwilling to or you receive a replacement car, a report would still be a good idea.

I am glad they found the problem. The G sensor as you call it is a perfect explanation for what happened to you. I would hope that they had checked for codes the first time you were in, and it does not surprise me that there would have been no codes at that time. The sensor has to be failing at a moment the monitoring computer can compare its output with some value and see it is incorrect.

The issue should be considered resolved. It is not a common failure, and is within the realm of everyday failures I see as a technician. Your loss of confidence in the car is not warranted, but is no less VALID. I hope you can work things out with Nissan and your family.

This kind of thing is always going to be happening. Cars are becoming more complex but are becoming far more reliable nonetheless. Switching to a different car of any make is unlikely to statistically improve your chances of experiencing or not experiencing another failure.

If anyone reading this has a similar problem, try to remember to switch off the VDC (or traction control) switch . This should disable the offending system (theoretically). On my 2012 it is the upper left button of the larger buttons below the trip computer (smaller) buttons.

This same situation has happened to me twice. Once today and once two months ago. Both times I was traveling about 45mph and going around a curve and had let off the accelerator when the car braked hard and turned to the left. I didn't touch the brake pedal either time. I am taking the car to my dealer tomorrow and will tell them about the G-Sensor. (?). I will post my results here when I get my car back.

2013 Nissan Leaf S - Leased

ColoradoBlue said:

This same situation has happened to me twice. Once today and once two months ago. Both times I was traveling about 45mph and going around a curve and had let off the accelerator when the car braked hard and turned to the left. I didn't touch the brake pedal either time. I am taking the car to my dealer tomorrow and will tell them about the G-Sensor. (?). I will post my results here when I get my car back.

2013 Nissan Leaf S - Leased

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Happened to me and almost ran me into a wall at 60. Hal took over for no reason and decided a drifting session was in order.

My Wife has had an issue like this 3 or 4 times while on the freeway. It happened yesterday, so we dropped the car off at the dealer today.

the dealer said they would test drive it. seeing as it only happens every once in a while, they won't find it.

Aren't there diagnostics they can download that will tell them the last time the Traction Control System was activated? (My guess is that the TCS is activating randomly)

Having the front vs. rear tires at different diameters can trigger traction-control/stability control events because the system detects different wheel rotation rate and interprets this as slip/skid event. Keeping up with tire rotations is a good idea, and also if replacing worn tires, replace all 4 at the same time, imho.

Are these all Model Year 2014 cars?

VDC (vehicle dynamic control and traction control) is overly sensitive on the LEAF and on several other vehicles I have driven. I have had the VDC on both 2011 and 2015 LEAFs kick in several times on freeway ramps with expansion joints. Each time, it required quick steering corrections to maintain control in situations that should not have been situations. It is scary when the car applies the brakes in a corner when there is no need and when I am holding the accelerator pedal steady. I have also had SUVs engage VDC when driving on icy roads with some wheels breaking through to pavement. These experiences have made me decide to keep my existing vehicles that don't have these features as long as I can keep them running.

After having the brake assist kick in on the 2011 when it was almost new and having Nissan tell the dealer it was normal, I did some testing on empty roads and found that you can always get the brakes to release by lightly pressing the accelerator pedal after releasing the brake pedal. I have learned how to tolerate and manage the nanny features on the LEAF, but I still wish for a way to turn them completely off.

Gerry

ColoradoBlue said:

This same situation has happened to me twice. Once today and once two months ago. Both times I was traveling about 45mph and going around a curve and had let off the accelerator when the car braked hard and turned to the left. I didn't touch the brake pedal either time. I am taking the car to my dealer tomorrow and will tell them about the G-Sensor. (?). I will post my results here when I get my car back.

2013 Nissan Leaf S - Leased

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The problem turned out to be the tires. I was running Hankook i-Pike winter tires. Standard size. Front and back. When I took the car to the dealership, they could duplicate the issue all day long. They contacted Nissan who had them run a myriad of diagnostic tests. Nothing found. Then, they replaced the Hankooks with my original tires and the problem went away. Haven't seen it happen again in over 6 months or so.

They didn't give me any technical reason. Nissan just told the dealer to tell me not to put the Hankook tires back on the car.

I returned the tires to Discount Tire and they immediately asked what tests Nissan ran on the tires. Were they out of round or was a tire separated? Unfortunately, the dealer didn't care what the reason was. They just wanted to make sure the issue was resolved.

Discount Tire did give me a credit based on what was left of the tread.