My wife’s 2011 E350 wagon is having an issue with the vehicle recognizing her key fob. It started as a message on the dash while driving and was initially intermittent. It is now continuous, requiring her to insert the key in the ignition every time to start the vehicle. In addition it is now difficult to lock or unlock the vehicle using the fob. You have to walk around the vehicle continuously hitting the lock/unlock button until you can find the right spot that it will receive the signal. Previously we could lock/unlock from inside the house 30 ft away.

The car came with 3 key fobs when we bought it. So logically I switched the fob and put in a fresh battery. I tried all 3 key fobs and continue to have the issue.

This leads me to believe it may be an issue with the antenna or ECU receiving the signal from the fob. Has anyone else had a similar experience, or any additional insight?

 

Check if radio getting solid AM/FM.

 

AM/FM signal is fine

 

3 key fobs ? It must be 2 , not 3 at least I have not seen 3 key fobs working all the time . Besides, when you see the message " key fob not recognized" just try these :
1- Press unlock button on the key fob
2- Press lock button on the key fob
3- Press unlock button on the key fob

Please press these buttons once at a time

Mine acted weirdly after key fob battery replacement, I tried the trick above and it's finally started to work flawlessly since then

 

The Engine Control Unit is not involved with the keyfob security handshakes.

Report to the local Mercedes Dealer for a coin cell battery service.

In the mean time insert key fob in key slot works safely to keep ignition active.