The car slowed down on its own today

[Ferdball]

My wife drove home from work today, the first time driving in the rain. About 5-10 minutes in she experienced unusual acceleration. Seemed like it sped up without her really pushing the gas and then didn't immediately slow when she pushed the brake.

She went to hit the wipers, but accidentally hit the cruise control. The speed got stuck at 55. She tried to accelerate but wouldn't go higher, then the car started to decelerate while on the freeway from 55 down to 35. Had to pull over to get out of traffic. There were no alerts on the dash.

Started again okay, but the car started to slow down again. Because she was in heavy traffic and was only going about 15 miles/hour, the car slowed to 0 before she could pull all the way off road, so she was stuck in traffic and unable to move. Tried to push gas and cruise control and went through dash buttons to figure out why stopped. After a few minutes noticed that the gear selector was in Neutral. She didn't change it to Neutral, but it was in Neutral. She was able to selected Drive and was able to finish her commute without further incident.

So, we're a little concerned with this odd behavior. I drove it a bit after she got home, but I couldn't get any of these issues to replicate.

Do you think this is something that can be checked? Will any diagnostic codes be saved? What should we do?

 

[mddg]

I'm sure that was quite frightening for your wife. I would take it to the dealer just to check it out, but it seems there are two issues here that may be responsible for the problem. Both the cruise control and the gear selector sticks are placed near where one usually expects and finds the wiper or headlight controls in most cars, i.e. around the steering column near the steering wheel. I had brought this up with the salesperson on my first trial of the B-class. He agreed but said the same configuration is used in much of the Mercedes line. My wife has also accidentally tapped the cruise control a few times already but figured it out quickly enough to avoid problems. I have a whole litany of complaints and suggestions about the user interface, but the stick placement is one of the more egregious problems.

 

[Ferdball]

Yes, the second time this happened, the gear selector was in N. So there's a good chance that she inadvertently hit the gear selector with her right hand.

But the first time it happened, she said that she accidentally hit the cruise control. Even if she did, there's nothing on the left side of the steering wheel that could cause this issue. The accelerator or brake pedal will override the cruise control. So, at least the first instance is a mystery.

 

[sendler2112]

I wonder if the inadvertent application of the cruise control combined with the collision prevention assist front radar caused the car to take control of the acceleration. I have a feeling that that it will never happen again as long as no driver will grab the wrong levers.

 

[Ferdball]

I wonder if the inadvertent application of the cruise control combined with the collision prevention assist front radar caused the car to take control of the acceleration. I have a feeling that that it will never happen again as long as no driver will grab the wrong levers.

That's probably the best explanation. She didn't notice the orange triangle on the left side, but then again, in the heat of the moment I probably wouldn't either.

 

[wtzouris]

Once cruise is SET, tapping the same stalk up or down increases or decreases the set speed by 5 mph, so it can get confusing unless you are expecting it. Pushing the stalk away from you cancels cruise. It sounds like inadvertent use of the cruise functions. I agree the ergonomics are not ideal, these stalks are not easy to see, and there is no Master ON/OFF for cruise control which I think every car should have on the dashboard.

 

[Ferdball]

I don't think it was cruise related, because she said the accelerator pedal wouldn't work. Cruise would never disable the brake or accelerator. My best theory is that she accidentally changed it from Drive to Neutral. I've done it myself.

 

[padamson1]

I don't think it was cruise related, because she said the accelerator pedal wouldn't work. Cruise would never disable the brake or accelerator. My best theory is that she accidentally changed it from Drive to Neutral. I've done it myself.

I think this is a major issue with the transmission control on the steering wheel in the same place and shape as the windshield wiper that is in every other new car on the road today. They should've used something noticeably different like a 70's like large, locking automatic knob control (pull to move) that also operates distinctly differently than any other wiper control. This way people who switch between vehicles and use the push down for single wipe feature won't accidentally put the car into neutral. Better yet move the four position switch below climate control sideways gear shift or pendulum like a golf cart, (so there are still room for the 3 cup holders) with some sort of locking feature for safety.

Since it mists a lot in Portland and I often drive my wife's car, I reflexively shift into neutral about once a week.

 

[Ferdball]

Once cruise is SET, tapping the same stalk up or down increases or decreases the set speed by 5 mph, so it can get confusing unless you are expecting it. Pushing the stalk away from you cancels cruise. It sounds like inadvertent use of the cruise functions. I agree the ergonomics are not ideal, these stalks are not easy to see, and there is no Master ON/OFF for cruise control which I think every car should have on the dashboard.

But I do love the one touch on for cruise, and the 5 mph increments for each touch after that. Very thoughtful and efficient and ergonomic. But yeah, the stalks are sometimes subject to misapplication.

 

[Starshoes]

My wife was driving on the freeway and the car made a jarring thump like it struck something, went into Neutral and rolled to a complete stop. Wondering if this has happened to anyone else. She was able to restart the car and getting it rolling again, but that wasn't much consolation as cars whizzed by her at 70MPH. I read that the Tesla-powered Toyota Rav4 EV's were recalled for an identical issue. Some even speculated that the same issue would pop up on the B-Class ED. It has.

 

[tom]

My wife was driving on the freeway and the car made a jarring thump like it struck something, went into Neutral and rolled to a complete stop. Wondering if this has happened to anyone else. She was able to restart the car and getting it rolling again, but that wasn't much consolation as cars whizzed by her at 70MPH. I read that the Tesla-powered Toyota Rav4 EV's were recalled for an identical issue. Some even speculated that the same issue would pop up on the B-Class ED. It has.

If her foot was on the accelerator going at highway speed, then if her hand accidentally moved the drive lever to Neutral, it would be logical to experience the sudden jarring thump as you described. Is this possible? Have you or your wife seen this problem again?