i do not have an E70, and do not know the location of the sensor... sorry...

Do not count on the dealer to do things correctly... and where are you taking the car for diagnostics? a dealer? i can guarantee you, that he will tell you that you need to replace several modules - he will start with one, then will move to another one, and at the end of the day, you will be out of $1500 and your alarm still will not work...

The dealers are module swappers, they do not do "bench" repairs any longer... You are better off to talk to an Indy (that is also a hit or miss) or do some of the troubleshooting yourself, if you are mechanically capable...