I've had a little search in the forums but I can't seem to find the issue that I'm having, I'm sure I'm probably not looking properly and would appreciate it if anyone could direct me to the right place if this issue has been brought up before.

I'm a noob to BMW and noob to this forum so forgive me if my etiquette is not up to speed! I brought an 03 525i about a month ago, damn I've been in love with these for years and was finally in a position where I thought I could somewhat afford it. Somewhat being the key word...

Randomly the other day, the key fob has stopped unlocking/locking the doors and opening the boot. It's a diamond shaped non-ca key. None of the functions work on the key and when I open the door manually using the key, the alarm goes off and I have to put the key in the ignition to stop it. My radio works fine, doesn't cut out, my central locking from inside the car works spot on and it works to auto lock upon take off. So after a bit of reading I'm guessing it's not the diversity antenna? Or am I wrong? Could it be the battery in the key fob? I have to admit, the lock function on the key before was temperamental, sometimes would work, sometimes wouldn't, sometimes the lock button would open the boot!

I've checked the fuses near the battery and they seem fine, battery seems okay (although there was some water in the bottom, only a few mm though, the other day), all been dried now. I'm not sure what this could be?

Hope you have enough information to help, thanks!

 

google search "diversity antenna e60"

 

With 2003 car and likely original key, the battery in the key probably is near end of life.
If you have second key, try with that key. If not, buy a new key from the dealer.

You need to investigate further about the water in the trunk. Remove everything from the trunk - including the spare tire and the foam padding under the tire. Look at the electronic modules tucked inside that foam - see if water/corrosion on any of those modules.