2004 E320 Key Problem
 

I recently purchased a 2004 E320 Wagon. After I got her home I locked her up using the electronic key. The next morning the electronic key would not unlock the system so I used the metal key which set off the alarm. Changed the battery in the electronic key which did not improve things. I then decided to purchase a new key.

Initially the new key worked well, for about three cycles! The last time that I was able to make it work a warning popped up that said something about the battery but the screen changed to "take it to a service station" so I wasn't able to get all of the message.

Any help or suggestions would be deeply appreciated. Thank you in advance!

Check the vehicle battery voltage, I've seen batteries that lose a cell and end up with a 10 V battery. This can scramble electronics.

This car might have a 2nd battery for the braking system, I'm not sure.

Many auto parts stores have a remote battery display and a tester for RF and IR remotes so it would be a good idea to see if the remote is consistent.

I'd think that there would be a way to scroll through dash error messages.

Just be thankful it starts the car!