Every once in a while, the car won't recognize a Keyless Go function. Sometimes it's a failure to unlock a door, other times it may be the ignition not recognizing the fob. This is nothing new, nor is it specific to the W205. If you search, you'll find many complaints involving this going back several years and covering all models of Mercedes vehicles with the Keyless Go option.

My first C300 had the problem, my long term C300 loaner had the problem, and my new C300 has done it a few times as well. Sometimes it resets itself in a minute or two, other times a simple press of the unlock button may bring it back to life. My wife just inserted the emergency key into the trunk slot, and that reset the system. (The new style emergency door slot is almost impossible to access.) I have changed batteries several times, but that doesn't provide a fix.

It is a nuisance, and I am surprised this type of electronic glitch has persisted for so many years. I believe the manufacturer is a company called Marquardt (?), and they have been making this for Mercedes for quite some time.

So, has anyone ever been able to come up with a reasonable explanation as to why these failures happen? The RFI excuse, especially smartphones, may be theoretically sound, but it doesn't explain the many times I've seen this happen with no outside devices present. Has anyone been able to come up with a fix for this? The system, and the antennae layout, have been changed over the years, yet the problem persists.

I have some background in electronics, and this has always felt like a receiver issue to me. It's easy to shield against low level RFI, so I don't know why this is still a problem.

 

The singular time I had this issue it was resolved by using a fob key press. I suspect as you can disable keyless go on the fob that I'd done this by accident.

I now carry the key in a pocket where it can't be pressed and I've had no further issue.

 

The times I've experienced it, the fobs were active but weren't being recognized by the car. In many cases, they started working again on their own after a few minutes.

 

It's happened to me three times in about the 3 months I've owned the car. No idea what causes it or why it seemingly fixes itself. Two of my lockouts lasted from 2-5 minutes, but I've had one last about 30.

On the 30 minute lockout I used the smartphone app to unlock the car and the key to start it up and drive home. I do wonder occassionally if my workaround caused the issue to elongate past the typical few minute period. Haven't tested that theory yet though.

This issue is easily my largest frustration with the car. But its one of my few so I feel relatively fortunate compared to some of the others.

 

Keyless Go has a mind of its own. I can touch the handle and nothing happens. Touch the rear fender and the doors pop open

 

Today when I was leaving a store my car would not start and I received a message on the center dash: Remove Smart Button and Insert Key.

I did that and was able to drive off.

I saw an earlier post and thought maybe I deactivated the key fob when it was in my pocket. I did a test when I got home and if the key fob is deactivated I get a message saying Key Not Detected.

 

I had a little trouble early on (build date, 12/23; delivery date, 02/07). I had a couple failures to unlock with a touch to the door handle and one "Remove Smart Button and Insert Key." I don't remember the order of the failures. The failures to unlock automatically were resolved with use of the fob. The "Remove Smart Button and Insert Key" was successful. Since then, no trouble.

One possible explanation: after these difficulties and reading about people's problems with this in MBWorld, I started keeping the fob in a pocket by itself, no change, no key ring, no nothing. Previously, I kept the fob on my key ring (just two other keys) with the fob of the phone home feature of my LoJack.

 

Also replace your keyfob batteries with fresh ones

I know the car is new but the batteries may have sat on a shelf for years prior to first use