hello, I have 530d 2003, sometimes my car lock, but sometimes I need to manually. Mostly it unlocks in cold weather.

All 3 keys have this problem
I checked fuses

 

I find the electronics in our cars (and in all cars really) act funny in extremely cold weather. How do they work in normal temperatures?

 

Perhaps a battery issue? How old is your battery?

 

In what state is your battery? Cold weather really diminishes battery capacity (up to 50% capacity is lost at -20 C), therefore if the battery is reaching the end of its useful life, that could be your problem.

 

I have had similar problems with my 05 e60. When I first bought the car only one key worked if I had it very close to where the antenna sits(top right corner of rear window on sedan, above rear window in the middle on estate). The other key didnt work at all. My local bmw specialist did a diagnosis test and found that the keys worked like they should but it was most likely the antenna, they replaced this one and then everything worked fine, I could unlock the car from far away. But now lately only one key works, and it varies how close to the antenna I will have to be, I think it depends a little on the temperature like said earlier in this thread. My local bmw mechanic tested the keys and found that both batteries were bad.

When all 3 of your keys have this issue I would think that the antenna needs replacement, since its very random that all keys should fail at the same time. Do you have bmw shops nearby? They most likely have a key range tester. Either they find keys are good and they need to replace antenna or something else, or the keys are bad and need new batteries. You will have to be able to solder in order to replace the batteries, and batteries can be found cheap online.

Hope you find a cheap solution!