I have replaced both crankshaft sensors and they are pretty easy to do. If you are planning to do this yourself, I suggest you buy the parts from BMW dealer, DO NOT buy it from the internet just because it is cheaper. I had my replaced but driving for a month the check engine light came back on then returned the parts and get the new version parts still - same thing happen. So I decided to take lose and just get the parts from BMW dealer for a little bit more. Now my car is driving like new car. Below is the link that will show you how to replace both parts.