Okay, I'd gotten used to my driver's door keyless entry working only intermittently. When I'm with my wife or daughter I open the passenger door first and that works for me! Recently I was at the dealer for an oil change and they replaced all my key batteries: both W209 keys and the W205 key for my wife's car. Never have I had batteries die faster than these! Once in the car I see "Please don't forget your key", then "key detected in vehicle", then, when I press the Keyless Go button "key not detected in vehicle." For a while, I just stuck the key in the ignition and turned it, like Fred Flintstone and Barney Rubble used to have to, lol. Lately though, I've been just repeatedly pressing the Keyless Go button like a frustrated Windows 7 user pressing Enter, and, lo and behold, it starts! Typically however, a few minutes down the road I'll see the RED alert "key not detected."

2 questions:

1. Might my Keyless Go be somehow dying, like my driver's door keyless entry?
2. Where inside the car is the key detected, so I can wave the key near it when the red alert comes on?

 

Does this happen with both keys?

 

yes, and I changed the batteries in one and it still behaves the same...

 

I'm having the same problem on my 2010 E550 Coupe, I switched the battery, now my keyless entry in not working, while my keys are in my pocket?

 

Keyless Go should be called No Go. Both cars I owned with keyless go had expensive problems. Deal breaker for me on a used car. YMMV