Replacing the Final Stage Unit

Up until two weeks ago I’d never heard of a “final stage unit” (FSU). And this is one reason I love the internet, because my car needed a new FSU, and I didn’t know it.

But the tech geeks on the BMW forums knew about it. Even better, they could describe a car’s behavior when the FSU needed to be replaced. For months, my car’s heating and cooling system has been erratic. Most days it worked just fine. But every so often it would turn itself on and off while the car was parked which drained the battery. FSU

I asked a number of gearheads at work. Could be the electrical system. Or maybe I needed a new battery. But nothing specific.

Google to the rescue.

I was about to take my car to the dealer when I searched the internet for heating and cooling system problems for my car model. Within a few minutes, I found a number of owners describing the same problems my car was experiencing. Nearly every post pointed to the FSU or the “blower motor resister”. It took me a while to figure out the the FSU and blower motor resister are the same part.

The BMW dealer wanted $400 to replace it. One independent shop would do it for $300. But several forum members had installed the part on their own. Using a link to an shop that carries OEM parts I bought a new FSU for $67 shipped. Once it arrived, I followed the detailed instructions from the same forum. That helped. But it was the pictures member had posted of their own repair job that helped the most. I was able to see the best way to get at hidden screws. I learned that by removing one vent, I’d have better access to the FSU, which was positioned awkwardly under the passenger’s side of the dash. Dozens of tips made the difference for a rookie mechanic like myself.

Most forum members were able to complete the repair in two hours or less. But those estimates came from owners who do a fair amount of work on their own cars. I’m good with computers, and those skills don’t translate well to cars. So I doubled the time and figured I’d need at least four hours.

At one point, I was sitting on the floor of my garage surrounded by my glove box, screws and other parts I can’t begin to describe let along tell you what their purpose is. I took special care to keep the screws close to the parts that fell off when loosened by my Torx 20. At one point, I felt overwhelmed and went inside to stare at my computer screen until I regained the confidence that I could put everything back together. It’s one thing to have a few screws left over after assembling a bookcase from IKEA. It’s an entirely different scenario to be dropping car parts along the freeway.

After a number of Diet Coke breaks, a few pep talks, and timely encouragement from my son, I replaced the FSU and put my dash back together. My prediction was right: it took just over four hours. My heating and cooling no longer acts like it’s possessed by demons. Every screw found a home, and I didn’t have to explain away any left over parts to Kim.

This is one reason I love the internet.

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