This is for an upgrade from the stock E46 AUTO DIM Mirror to the later model years AUTO DIM Mirrors with the enhanced features. My car also has RAIN SENSOR but during the DIY I realized the Rain Sensor module has no business with the mirror other than sharing the housing. So I will state here that this DIY is workable regardless of rain sensor or not.
This has to be the easiest DIY for the E46 provided you get your hands on a good mirror that has all the trimmings uncut and unspoiled. There is no tools required for this DIY other than opposable thumbs, a brain and a dental pick.
I lucked out and found this 2006 E90 Premium Package Mirror on eBay for under $200. It came in new condition with the connector still attached. Make sure your mirror also come with its connector harness attached or you will have to splice wires and possibly trek down to the dealership to buy a new mirror harness for the upgraded mirror you are installing.
From 2001 to now BMW has not really changed their mirrors. Once the mirror that is currently in your E46 has auto dim then the connector harness will be the same for all later year mirrors with auto dim as well as other mirrors with both auto dim and the other features. I believe this is regardless of what model car you get the mirror from (IE. a 2008 7 Series Sedan's mirror should fit in a 2001 E46 sedan)
My new mirror came with the pigtails of the E90 connector cut from the car and not cut from the mirror. So I was able to un-clip the E90's in-car-connector's wire pigtail leaving just the mirror and it's connector. Which I was hoping would also connect up to the E46's in-car-connector.
Start the DIY by removing the current mirror. The rain sensor housing un-couples from the center. Press your opposable thumbs against them and spread the shells apart. It should give you no trouble whatsoever.
Underneath you will find the mirror's neck and, if you have it, the rain sensor module that sits against the glass and away from the mirror. So don't touch it.
Next up you will un-clip the old mirror's connector from the E46 in-car-connector and remove the mirror from the car. Swivel the neck on the top hinge towards the passenger side until it pops out. It may be stiff so give a slow firm pull. The Dealership's DIY Manual says turn it about 45 degrees to release it. Again it should give you no trouble.
Compare the connector clips of the new and old mirrors. They are the same.
Attach the new mirror. If your E46's in-car-connector is different than that of the new mirror's then you need to find a E90's (or E46 that came with Anti Dazzle) in-car-connector. The dealer sells a retrofit kit or harness connector just for this thing.
Screw the neck of the new mirror onto the car. This should be no problem.
Now you are almost done...
here is where you can test the new mirror once the harness connectors are all connected. turn the car on and make sure the compass lights up and when you press any homelink button a small yellow indicator lamp blinks.
Time to finish up by replacing the housing. I noticed the housing that came with the new mirror was the newer, bigger E90 style with vents and all. Not sure what the E90 was packing under all that plastic...
I tried to get cute, but it didn't look pretty. lol.
The E90 housing also fits onto the E46 but the E46 rain sensor footprint didn't match up properly...
Most of you buying mirrors may not get any E90 (or whatever) housings with the mirror so don't worry about getting this with the new mirrors since your old E46 housing will work and fit over any of the newer mirrors.