Sorry to bump such an old thread, but...

I connected up to my new trailer (with LED lighting), and I had all the symptoms mentioned in the thread (fast blinking, lights blinking even when car is off, and the rear PDC not disabling when the trailer is connected). I then tested with a trailer with conventional lighting, and everything behaves perfectly.

In the absence of a better solution, and to get everything functional, I replaced the tail/stop/blinker on my new trailer with old fashioned bulb units. At the risk of stating the obvious - the "always on" lights have no effect on the behavior. I left those as LEDs. Everything now works the way it should - normal blink rate, no flashing when car is off, rear PDC is disabled when trailer connected and immediately re-enabled when trailer is disconnected.

I don't think it has been mentioned, but if your blinkers are flashing too quickly when the trailer is connected, chances are the X5 has no idea a trailer is there (which is the reason PDC isn't disabled properly). In addition, this almost certainly means that the trailer stability control program won't be enabled.

Given that this thread is over a year old, has anyone come up with a clean solution for the LED lighting issue? A resistor wired inline prior to each LED tail seems like the most cost effective solution available currently.