Braking Lurch when almost stopping

[snowds]

I see that a couple others have experienced a lurch when the car is very close to stopping. Mine seems to happen when I'm really slow, and let go of the brake, then apply it again, though it has been very difficult to reliably duplicate. Has anyone who has this issue figured out how to duplicate it with a consistency that can be demonstrated to the dealer?

 

[TheStig]

I think I can feel what you are talking about. There is a odd feeling as you slow down to a stop sometimes, hard to pinpoint exactly what it is and certainly not easily repeatable.

What I think I feel is the motor switching from regen to creep as you get down to a near stop.

As you slow from speed the motor is acting as a generator recapturing some charge, at a certain speed the car isn't moving fast enough to regen and the motor switches back to forward power to give the "creep" the enables slow forward motion under light braking at low speeds. That switch point from regen to creep is probably what we are noticing.

Couple that with the different levels of regen depending on the gap the radar has measured to the car in front of you and it certainly isn't consistent. Not sure anything is really wrong with what I'm describing, just an adjustment from a gas powered cars more predictable behaviour.

 

[snowds]

I know the surge you're describing when it switches from regen to creep; it's not that one. That surge is barely noticeable compared to the one I'm talking about which almost feels like the anti-lock system is kicking in, and is not at all subtle (passengers notice it).

 

[BCKator]

I too have experienced such issues (lurch & jerk) at times when coming to a stop.
It's near impossible to recreate on demand so I've never brought it up with my service rep.
Like Stig, I attribute it to road conditions, me trying to feather it off perhaps not perfectly, and the car having trouble trying to decide between creep and stop.
Not sure if re-gen mode is a factor or not. FWIW, I have the radar-based-regen option and I usually have mine in the default/auto mode.
I don't consider it a huge deal but do think that there is room for improvement in the software which I hope someday will come.

 

[snowds]

Thanks BCKator. I usually drive in D+, so doesn't look like it's related to mode. I will spend some time trying to come up with a protocol that reliably duplicates the issue. If anyone figures it out, please post here.

 

[snowds]

Anyone figure out how to duplicate this yet? I have noticed that it happens most often during a firm stop on a decline, or firm stop with wheels slightly turned.

 

[JeffRay]

I get it once a week or more. Usually when coasting to a stop and I need to brake to not hit the car in front because I misjudged. It does feel like ABS but going so slow doubt that is going on. More likely, the brain thinks regen but is surprised by brake application by driver. It is something that should be mentioned to service advisor as it would be a software fix if brain confused. Unfortunately, the advisors don't know anything but can be asked to pass along to MB service central.

It has never happened to me at speed. Total incidents around 20+ over six months.

 

[wtzouris]

I agree with Jeff in NYC, it happens when creeping to a stop, downgrade, at very low speeds like 5 mph. It's annoying but not dangerous. I've had it happen 5-6 times in 6 months/6500 miles driven. This is different from the ABS system brake check that occurs every morning on the 3rd stop sign I encounter. That's way more subtle.

 

[jsvish]

Similar experience here. Jerk/lurch when break is applied while going slow. I have seen this at least once a week. Havent talked to the dealership, look like a common problem.

 

[phototrek]

Same here. The whole commute home was very jerky, at least five times.

 

[Bgrade]

So I have been dealing with this issue... Feels like the transmission. The car also severely shakes shifting between park drive and reverse. We also had the trany loose power once while driving and several time early on a warning do not shift gears visit dealership light was displayed.

The dealer has performed software updates and said they have fixed everything but it still lunges for on occasional stops. They now say its a characteristic of the car and operating as designed.

Easy to recreate... Roll slowly on a slight decline then apply the brakes coming to a short stop.

If anyone has more ideas on the cause or a possible solution please share.

 

[mkeeton]

My experience is that this seems to be related to the creep function that they have built into the car. At some point when coming to a stop the software must engage the throttle just a bit in order to activate the creep function. That seems to happen just as the car is about to stop and causes a lurch. If you stop completely, wait a second and then lift your foot off the brake you can feel momentary pause and then the creep engages. So, my theory is that it is the engagement of a tiny bit of throttle just as you are about to stop which then cause the car to lurch forward a bit and you have to then engage the brake a bit harder to complete the stop.

I wish they would get rid of the creep function. Makes it tough to brake the car to a complete stop smoothly. Our i3 has no creep and it works fabulously. In the Tesla you can choose to have creep or no creep. Wish we had the same option. I bet that would fix the lurch and make the car much smoother to stop.

 

[RGDavey]

I get a similar "shaking, lurching" whenever I'm close to stopped and have to apply more braking pressure quickly. Like when someone cuts in front at the last second. Happens every time and also makes the car do the same as you press the accelerator after the stop.

I'm taking my car in for the recall and will add this abnormality to the work order.