Stupid self-opening car trunk problem

I drive a leased 2019 MB C300 4Matic sedan (my employer is a Daimler subsidiary so I get a good deal), and with previous models this has happened on occasion as well. The current car is about a year old now, and it hadn’t done this yet, despite my carrying around the fob in my jeans pocket all year. The fob was redesigned for 2019 so I thought (and it seemed) that the problem had been solved.

But since it happened today, and on a rainy day to boot, I’m thinking maybe the fob having its “open trunk” button pressed inadvertently by other crap in my pockets isn’t the cause. Has anyone else seen this kind of thing, with Mercedes cars or otherwise? If so what ended up being the cause?

Yep. I don’t have a Mercedes, but after I got a new car it ended up with its trunk open in my carport several times. After playing around with it I concluded that the key fob was powerful enough to reach the car even when I was indoors and several floors up. I think I was accidentally hitting the fob when I was putting the key away in my apartment.

I ended up getting a small carrying case for the key fob and it hasn’t happened since.

Definitely not a Mercedes, but I had the same issue with my previous car, a Kia. It happened several times. I’m not sure what caused it, but I like to play with the fib in my pocket while walking from my car, so that definitely could have been it. The worst case when when the trunk was popped in my garage for a weekend causing the battery to drain. It also happened once or twice when parked at work. I learned to remove the keys from my pocket as soon as I got to my office. It was irritating definitely.

Thanks for the replies. The thing is, with previous models, it definitely happened like two or three times within the first year, but this time it took till the car was a year old. You’d think that if accidentally pressing the button on the fob was the cause, it would have happened before with this particular car. Just in case the fob is the problem, though, I’m taking it out of my pocket and setting it on the windowsill near the front door when I come in, as I ended up doing with the previous car that used the old fob design.

What kind of pisses me off is that my nextdoor neighbors didn’t think to knock on my door and say anything about it. But who knows, maybe they’re out of town for the weekend.

That was bizarrely similar to my experience. I bought the car used and had it for several years before the issue started. I wonder if as the battery in the fob went down it started sending winky signals or something.

I have an Audi S5, but have the opposite issue, if you can call it that. The auto-open function for the trunk, where you wave your foot under the bumper, seems to work about half the time, and only if you stand with Teutonic precision in precisely the spot the engineers determined was optimal. I don’t think I’ve ever used the key fob buttons for anything.

I had this issue on a Ford Zetec. The problem was nothing to do with the fob; the button you press on the boot (urgh, ‘trunk’) itself to open it was causing the issue. Basically water was getting into it and causing a short circuit. Since you mention it was a rainy day, the chances that you are suffering the same issue is, well, high.

I fixed it myself by removing the button in question, opening it up and stuffing it full of non-conductive silicone grease to keep the water out. Since the button is rubber, it had degraded a bit and was allowing water ingress. I could’ve bought a replacement button (they’re cheap enough), but already had the grease handy anyway.

This was over a year ago and I have not had this issue since. The electronics were simple, nothing more than a couple of wires so not much to be afraid of there. Hardest part was removing all the inside panelling covering the hatch to get at the button to remove it.

I have done this with my Kia as well. The buttons are easily pressed. I also did it with my Mazda before this car. I noticed it had more to do with where I put my keys (and fob) in my pocket and what I was wearing. Apparently when I sat to have coffee before going to work, my khaki pocket would bind a bit or something. And I’d shuffle outside a few minutes later and notice my trunk was slightly ajar before heading to work. The first few times this happened I thought someone had broken into my car. No, it was just my fob acting up in my pocket.

This is good advice. Or carry it differently, or even just in another pocket.