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Final Stage Unit Replacement

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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 for replacement.

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 straight out.

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.