As mentioned above, the battery in the key charges while it's n the ignition. We had problems with ours not synching and I asked the same question at the dealer.

What you should do is unlock the car with your working key, then use the one that doesn't work while driving and it should charge up again.

Interesting to read about the water thing though. As ours stopped working again recently, then worked for a while, and now doesn't.

 

Luckily our car went in for a service yesterday and they couldn't re-sync the keys at all.

In the end, they had to replace the unit as it has water in it. Now say it won't (shouldn't) happen again.

It's bad enough having to always go to the driver's door to unlock/lock the car, but the fact that the key wouldn't switch off the alarm until it was in the ignition was a right PITA.

It was such a chore as my daughter's car seat is in the opposite corner to the driver door, so whenever she was in the car it meant getting her to come round to my side of the car to wait in safety, unlocking it, having the alarm go off, sticking the keys in the ignition, taking her around to the opposite side, putting her in, then going round to the driver's side again to get in.

And as for getting her out it was equally problematic. No wonder we were all so much fitter in the old days.

 

I think my car is suffering from this same issue. Where is the transmitter located?

 

I had same problem with a 3 sereies. Could lock the car but often would not unlock on remote. Problem was ocassional and never hapend when service agent was trying to find the fault. Finally, after two years, it stopped working completely and they found is was a faulty receiver / arial that runs along the C pillar (on a 3 touring) which receives the signal from the key. Strange though, after fixing the problem with new arial installation, the range of the remote was never as good.

And have you ever noticed how holding the key against your head and clicking the remote lock / unlock really extends the range of the key. I cna open / ;lock the car doing this from at least double the range.(just a fun fact)

 

Guys, Looks like I am facing the same issue. I have 520d 2009 touring. I went away on holidays and when I came back I could not unlock car with either of the keys. I can unlock with the metal key but then the alarm goes off and have to put the keyfob in the ignition for alarm to stop. Please see the pic of the keyfob attached if needed.
Couple of questions:
1. Where can I find the transmitter/ receiver?

2. Is it easy enough to change, if needed?

Many thanks
Rahul

 

I believe the Key Antenna and receiver is under the Spoiler over the rear window?. Looking for validation from others. Check realoem.com J

 

My keyless entry also stopped working mysteriously. After a lot of searching this is a very common problem. The transmitter under the spoiler COULD be damaged, but another very common issue is severed wiring leading to it that runs above the headliner and through the hinge point of the hatch. That is what it ended up being for me, and I was able to fix it for about $30 with some silicone wire, solder, and a Saturday. The diversity antenna itself is around $270. Here are some helpful pieces of info I found to investigate the possible wiring issue.

http://www.snowspire.cz/staticke/E61-kabely.pdf
Touring Hatch harness fun

 

I also left the boot open in the rain yesterday and now my central locking remote is not working. Does it dry out, or do I need to replace the unit?

 

I would suggest popping the spoiler off and getting the plastic cover off the antenna amplifer - it's not that difficult to do, and you can spray down the circuit board with some electrical contact cleaner. You'll probably find corrosion on some of the terminals and pins. If you can't get it working, next step is a replacement. I've had to do mine twice now - 2010 model.

 

FYI, if you do have to replace it, get one from a 6 series. They have a different part number but fit and work identically. I did this because on eBay the E61 antenna amplifiers were extremely expensive and yet the 6 series ones were much cheaper.