Stan, when you press the buttons on the key, do you get a confirmation light on it (just wondering if the key is powered-on at that time)?

 

Could this be a door handle issue (sensor) rather than a key issue?

 

Yes, the fob light does come on. This also indicates that the battery is good.

It's probably not a door handle sensor, since at times the ignition also won't recognize the fob. I've had the doors open, then have the ignition not detect the key; and also the doors not work, but the ignition is fine.

These issues are always temporary, and everything goes right back to normal when the problem clears. My car had no key fob problems until a few weeks ago ... then it just started happening. I have changed batteries on both fobs, but that made no difference.

I think there is some sort of intermittent issue with the receiver in the car itself. I don't think this is being caused by anything in the key fobs.

 

I dont know if there is an issue with the W205. But it is more likely that it is operator error.
You are probably doing one of three things wrong... maybe all three.

1. Do not place your key near another transmitting key (second car/spare key) or near a phone.
2. Unlock the car before you pull the handle. (just like any car, you have to unlock it before you pull the handle) you unlock the car by placing your hand inside the handle, when the car unlocks, you can now pull the handle.
3. Do not touch the outside of the handle when trying you unlock the car. Only place your hand inside the handle to unlock the car.

If you ensure that you attempt to open you car correctly and it still doesn't open then you should take your car in for service.

I hope it works for you. Good luck

 

No user error involved on my part ... I'm sure of that. I've had the car for five months and am pretty familiar with how things work on it. I also don't carry a smartphone or spare fob on me. How does this explain the failure of the ignition to recognize the fob? With no codes being thrown, there's not much a dealer can do.

 

Stan,

I think you live in some kind of weird, bleeding, electrical snafu vortex!

 

Have you tried the second key when the first one is acting up (to see if it's an issue with the key part or something in the car)?

 

I only have one key on me at any given time. The same thing has happened with both keys, so I don't believe it's related to a particular key.

This is not an uncommon problem, and many owners of the W205 have complained about it.

Recently, I had a C300 loaner while mine was in the shop getting the seat covers replaced. The Keyless Go on the loaner malfunctioned about four or five times a week. I replaced the CR2025 battery ... made no difference at all.

 

Not operator error. I keep my phone either in my coat pocket or in a different pants pocket from my key (learned some keys can scratch a phone screen the hard way). I always wait on the car to unlock before pulling on the handle and only touch the inside of the handle.

I feel as though taking the car in for service will be somewhat useless as this is happening intermittently and apparently does not throw any failure codes. I do, however, plan on mentioning it to my service rep when I take it in for the first service.

 

OK, It's fixed for now. Had the problem with a new to me (used) car delivery. CLS550 2014. Lots of complicated failures but after reading all this. I changed both batteries. Had to replace 2025's with 2032's. They are both 3V with the bigger number being fatter and longer lasting.

I just went out with one key at a time and unlocked and locked with the remote buttons. Then tried keyless entry and engine start, one key at a time, with the other far off. They both work now, the car says the batteries are low in both keys, so they've ben in my storage for maybe 3 years, so that very well may be true. So I'll change them out and see if that message goes away.

Solution: Wait. Unlock and lock with the key, and then do the handle/keyless entry method and maybe you will be as lucky as I am. For today.

I put the old skinny batteries in just to see, and one of them was dead as hell. So I put the fat battery back in and it works.

 

Just as a note, the solution for me was an eventual software update for a communications error code that the dealer was able to find. IF an error code was thrown, there is a TSB out for the software update.

 

Thanks. Great info. I'll keep that in mind on the first dealer trip for a failure. I bought the 72 month/100K mile warranty for just such occasions.