The budget refinishing of my Style 42 wheels will have to wait, as the media-blasting quote from the fellow on Craigslist that sounded too good to be true—$50 to $60 for the set of four—turned out to be, uh, too good to be true (“It’ll take me a while to get to those”).
I have a certain automotive iron in the fire that I’m not quite ready to reveal, so this week we’re going go to something more mundane and useful: replacing a Final Stage Unit (FSU).
Shortly after beginning to daily-drive the 2003 530i stick sport, I noticed that the blower fan had a mind of its own. It would switch on when I had it off, or run at a higher speed than that at which it was set, or continue to run after the car was shut off. This is textbook behavior of a bad Final Stage Resistor, also called the Final Stage Unit. I had one of these go bad on my old 1999 E39 sport wagon, and it literally drained the battery down to the single-volt level while the car was parked from nine to five at work. Because I didn’t want to come out in the morning or at the end of the work day to a dead battery, I installed a battery-cutoff switch in the E39. That worked fine, but I wanted the problem fixed.
The FSU is essentially a big computer-controlled resistor pack that allows the fan to run at less than full speed by putting resistance in line in the circuit, limiting the flow of current to the fan. And, as anyone knows from Ohm’s Law and Watt’s Law (or from my upcoming book), if you’re limiting current through the use of resistance, and if that resistance isn’t being used to perform useful work, it has only one place to go: heat. So the FSU has multiple pointy heat sinks on it, making it look like a something you might have seen in 50 Shades of Grey if they hadn’t gone soft and half-Monty and used only paddles.
The same FSU, part number 64 11 6 923 204, is used on the E46 3 Series, E39 5 Series, E83 X3, and E53 X5. It’s located up under the left side of the center console. It’s not terribly difficult to replace, though it’s a little tricky to take out. Google “E39 FSU replacement” and you’ll find any number of good guides on forums, as well as videos on YouTube.
The main issue to me was choosing whether to replace it with an original equipment (OE), original-equipment manufacturer (OEM), or aftermarket part.
Both the part number and the design of the FSU have changed several times. The current part appears to be German-made; it’s branded as Sitronic, though it appears that both Valeo and Bosch/Hella are actually the ones that manufacture the part for Sitronic. Online photos of the OE part show a sticker that has the names BMW, Sitronic, and, for example, Valeo on it. The dealer list price on the OE part is about $140, with discounted list as low as $110 through some Roundel advertisers.
But if you search Amazon, eBay, or your favorite parts vendor, you’ll also see the thing advertised as OEM, branded Hella/Behr or Valeo, for half that cost or less. A little web-searching reveals that although these parts are thus branded, some are German-made, but most are made in China, and are thus not the same as the German-made OE dealer part.
A few hours (well, more than a few hours—you know how this stuff goes) on web forums revealed that there appears to be a hierarchy of recommended manufacturers, with the dealer-supplied OE part first, followed by the OEM German-manufactured versions, followed by the OEM Chinese-made versions, and bringing up the rear, the you-don’t-know-what-they-are $20 eBay specials.
Now, people feel a whole variety of ways about parts, from “You violate the laws of man and God if you don’t use dealer-supplied OE parts” to “I spend as little as possible and will put anything in my car.” Me, I’m practical about this stuff; I’ll buy very inexpensive non-OEM parts from rockauto.com for things like hood struts. If they fail, they’re very easy to replace a second time, and they don’t cause anything else to grenade. The FSU isn’t difficult to replace; it’s more an issue of the fact that its failure can cause you to come out in the morning and find a dead battery.
My basic tack is to understand these things, know what the OE and OEM parts are, then price them at the dealer, on eBay, Amazon, and the four or five suppliers I consistently use, see what the cost difference is, and make an informed choice.
I looked on eBay and found, to my delight, four suppliers selling what was called a “New OEM Made in Germany Blower Motor Resistor” for about half of dealer cost. The photos clearly showed the label saying Sitronic, but with the BMW/Valeo part of the label cut off. That’s not unusual, and often constitutes the difference between OE and OEM (I’ve purchased OEM water pumps that appeared identical to what you’d buy at the dealer, except the BMW roundel was ground off).
So I ordered one from an eBay advertiser with whom I’ve had good luck over the years on this sort of thing. However, when it arrived, the part had no sticker on it whatsoever, and the box it was in had only the part number, followed by the letter H.
I contacted the seller, saying that because the part had no sticker, it not only wasn’t as pictured, I had no way of knowing if it was indeed as advertised, and thus I needed to return it. I received a prompt and professional reply from the seller explaining that the part was a Sitronic-branded German-made part, but the way in which the lot was purchased prevented him from selling it with the label. I was about to take him at his word, but then I web-searched the part number followed by the H, which was printed on the side of the box, and all of the links were to Chinese commerce sites. I thanked him for his response, but gently insisted that I’m sure he could see it from my side, and that I’d need to return it, which I did.
I then sent messages to the other three eBay advertisers who showed pictures of the same part with the same label, saying that if they were certain that the part they would send me had the label shown in their ad, I’d buy it. Two said no, the actual parts were unlabeled. But when the third said yes, I ordered his part. However, a day later, I got an e-mail saying the sale was cancelled, with the explanation that his original assertion was incorrect.
So that was it for OE.
I then looked for German-made OEM. A vendor on Amazon sold what was advertised as an OEM German-made Valeo unit, with a photo that showed the same razored sticker as the eBay ads. But it was listed as out of stock, with more arriving in a few days. I thought I’d wait it out, but whenever I checked, the in-stock date receded like water before Tantalus.
I gave it one more try. One of the parts suppliers I frequently order from listed, among other options, a unit branded VEMO, “made in Germany.” Another vendor showed an inexpensive unit as “OEM, German.” I contacted them and asked who the supplier was, and was told it was “CoolXpert.” I looked on several users’ forums for information on these vendors and found nothing. I posted a question but heard nothing back.
Enough. I paid the $110 and ordered the OE unit from one of the dealerships who advertise in Roundel. After researching all the data, it was gratifying to open up the package and see the full label on the part.
Here are the original part and the updated part side by side. You can see that the original has a metal base and large conical heat sinks, whereas the updated part has a plastic base and a larger number of smaller rod-shaped heat sinks.
As I said, it’s not terribly difficult to replace the FSU. You don’t need to remove the glovebox, as some videos say; you only need to remove the piece of trim beneath it, which simply pulls straight out, and the long trim cover on the right side of the console, which is held in place by one Phillips screw. Then you slide the piece forward and pull it out. This exposes the FSU, though it’s up and underneath. You can even look up at it and see if it has a metal base. If so, the odds are that it is the original FSU. The photo below shows it after I’d replaced it, so it’s showing the one with the black plastic metal base.
As the videos and how-tos tell you, the electrical plug into the bottom of the FSU needs to be squeezed on both sides and pulled out. If you can’t get it with your fingers, a pair of needle-nosed Vise Grips usually does the trick. Then there’s a plastic tab at the lower edge of the FSU that needs to be levered downward to draw the FSU out. I just use a screwdriver to pry the tab down and lever the FSU out. Slide the new one in, push the connector in, put the trim pieces back, and no more ghost-inhabited fan or threat of imminent battery drain.
Now, if only getting these Style 42s refinished was as easy.—Rob Siegel
Rob’s book Memoirs of a Hack Mechanic is available through Bentley Publishers, Amazon, and Bavarian Autosport—or you can get a personally inscribed copy through Rob’s website: www.robsiegel.com.
