Where is a crank sensor located 2004 bmw 745i

SOURCE: Where is the Crank Sensor '99 BMW 523i E39 Auto

are you sure you need the crankshaft position sensor changed. it is at the back of the engine i believe, but.....
check for a wet ecu first... read the note on e36...

the ecu compartment is under the windshield on the passenger side on E36

you gain acess to it under the hood....
this compartment gets wet, the ecu lays on a flat surface in that
compartment.

the bottom side of the circuit board gets wet and starts corrosion.

remove the ecu, take the bottom plate off, clean the bottom of the circuit
board with alcohol and a soft tooth brush.

you should be able to see the signs of corrosion or conductive build up.

this gunk bridges solder points doing all sort s of wierd things to your
car, including false sensor readings from asc/abs controllers and other
sensors....

all the way to engine failure and worst case burnt and shorted wiring
harness.

I'm on my 3rd ecu, took me and the repair boys a few years to figure this
one out.

BTW: i would get that ecu mounted above that flat surface, use some sort
of standoff to raise it so that it is not laying in the wet.

SOURCE: My dynamic drive inactive light came on what do it

YEAH CHECK YOUR BELT MINES DID THE SAME THING ITS THE SERPENTINE BELT