Final Stage Unit Replacement
If your interior heat/AC ventilation fan
either works intermitently or only at a single speed regardless of the
setting, you probably need to replace what BMW calls the "final
stage unit." It's part number 64-11-8-385-549 (new part number
64 11 6 929 486). Cost is under $100.
This is what it looks like.
It's a relatively easy repair. If you know
how to take things apart to access it, then it should take no longer
than about 15 minutes. Below is a quick and dirty set of instructions
The final stage unit is located to the
left of the glove box, under the center of the dash near the firewall.
Access is from the passenger side of the
car (driver's side on right-hand drive cars.) You'll first need to remove
the carpeted bolster that runs along the side of the center console
(on right-hand drive cars, you'll need to pull the plastic panel over
the pedals to do so). Remove the visible screw and then slide the bolster
toward the rear of the car to release the clips that hold it to the
center console. There are two clips - one near the front, and one near
the rear. The picture below shows how the clips are positioned and fit
into the slots. Once the clips are clear, the bolster should come off
easily. Don't force it. If you break the clips the bolster will not
stay in place and it's almost impossible to fix them. Pulling the plastic
panel under the glove box also will give you more room to work (pulls
straight out toward you).
Once the bolster is off, look up under
the center of the dash, just above the transmission tunnel. You should
be able to see the plug for the unit as shown below.
The plug releases relatively easily; however,
the unit itself is held in place by a black tab at the bottom that's
difficult to see. To remove the unit, press down on the tab while pulling
A closer view of the tab is shown below.
The new unit slides right back in. Reattach
the plug and test. Assuming that it works, replace
the bolster and you're done.