Transmission Surging Fix
First time on a forum in a while, but had to get on since many of you have experienced exactly the problem I encountered beginning early 2009 with my 2005 545; transmission surge. Took the car in 3 or 4 times (under warranty) with little to no success. Finally, with 1 week to go on my standard warranty, the transmission was replaced with only 46k miles driven. Very frustrating, but the new transmission seems to be working well.
May not help those out of warranty, but the tech explained the problem as follows (please accept my layman's paraphrase):
The "surge," which feels like someone has run into the back of the car, may be a result of the "bands" slipping (using this term loosely). Basically, as the car decelerates (as in my case while coming to a stop sign), the transmission was still engaged in a higher gear (say 3rd), then when I accelerated again (needing 1st gear, for instance), the "slack" created resulted in a jolt once the gears re-engaged at the lower gear. Basically, the transmission is slipping.
On this thread, another user indicated a problem with the transmission error message indicating low fluid level. I've had the same problem for over a year. The BMW guys pressure tested the radiator on two occasions, and finally replaced a few hoses. Seemed the problem went away, for a while. Coolant is still leaking out from somewhere, however, but it seems to evaporate (thus the difficulty in finding the leak). I've grown accustomed to topping off the coolant every month, but it's getting old. My 3 series never had this problem in over 5 years. Any feedback would be appreciated.