Replacing the final stage unit/blower motor resistor (E39)

Another successful replacement here. A huge thank you to Elvis for starting the thread and including the pictures which were key to my success.

This defective part had plagued my 2002 540 for over six years with the standard on/off and speed fluctuations, but finally got so bad that the fans were constantly running when the vehicle was off, and so of course the battery kept getting completely drained.

I wound up paying $120 USD for the part at the dealer since it was a Sunday and they were the only place open that actually had the part in stock. No big deal, and at least the part was brand-new and not after-market.

One suggestion: use a strap-on head lamp when you are under the dash. It is so tight that trying to manage a hand-held flashlight up in there is a nightmare.

Thanks again!

Originally Posted by MikeD_540

One suggestion: use a strap-on head lamp when you are under the dash. It is so tight that trying to manage a hand-held flashlight up in there is a nightmare.
!

After 3 months of DIY, I finally ordered one off Ebay for $3.
I can't for the next time I need a light and a free hand.

Just fixed my 2003 BMW 525i. Thank you very much! I thought I had a bad battery, but upon further inspection, I found the blower was constantly running when the engine was off (It was such a faint sound, but it was there).

I just changed mine today only to discover that it wont turn off! Even with the ignition turned off the blower was still going. Any suggestions? Could it be an installation error? or perhaps a bad unit.

Did you buy a new FSU? I have heard of this issue when my FSU was going out and that turned out to be the culprit. Many people experienced the same thing. I had replaced my first with a cheap after market part and it was defective. Paid more for one at Bap Geon and it still works today.

My problem was opposite the fan would not come on at all.

The FSU must control the circuitry to the fan. Sounds like yours may stay open somehow with the ignition off keeping power supplied to the fan.

Originally Posted by greg1956

I just changed mine today only to discover that it wont turn off! Even with the ignition turned off the blower was still going. Any suggestions? Could it be an installation error? or perhaps a bad unit.

I had this same issue before I replaced mine, but it was fixed after replacement. Where did you purchase the part from?

Thanks so much for this post. I have cool air again.

I bought a cheap FSU on ebay initially that did not fix my problem. i bought another at Bap Geon and it worked well.

Another satisfied customer. Great original post. Nice to have AC again. The only thing was I couldn't get the new unit to click back in place so just wedged it in place. Hope it doesn't slide out.

never done one on a wagon............but hope it works!

Originally Posted by E39swagwag

The only thing was I couldn't get the new unit to click back in place so just wedged it in place. Hope it doesn't slide out.

Same thing happened to me.
I think it's fine, as there's nowhere for it to go anyway.
Been fine for months...

one of the best DIY posts. Thank you!!!

happy for you!

Originally Posted by EconoBox

Same thing happened to me.
I think it's fine, as there's nowhere for it to go anyway.
Been fine for months...

I had this happen as well, and it ended up being the wrong part. It worked, but when I went back in to the shop I was told it was the wrong part. They gave me a different one that still looked somewhat similar and it worked flawlessly.

Maybe your model requires the one they had originally given me.

you know the old saying: "Don't fix it, if it ain't broke".

I have a 2008 528i and have similar problems with the a/c. The battery in the car went bad and I have replaced it. Right before I replaced the battery the a/c quit working for about half a day and then magically started back. Then a day later it quit working again. I then replaced the bad battery and the a/c still did not work. I took it to a auto air place and they said they think the blower motor is bad, but not sure. They told me to take it to the BMW dealership. Of course I am trying to avoid this because I know they are going to charge me some outrageous price to look at it and no telling what to fix it. Anyway today it magically started working again, after not working for about 5 days. Does anyone know if this final stage unit has been known to go bad on the E60? Thanks

I believe EAC Tuning offers an FSU for the E60..............and if so, I assume one could go bad. I just bought an E60 within the last month, so I am still trying to figure it all out. I replaced the FSU on my E39 without issues. I suggest you search the E60 threads for an answer.

man thanks that was easy

Thanks for the instructions. Everything worked as mentioned on my 2003 530ia. Took about 45 minutes for the whole thing - fastest repair ever for anything on this car.

BTW, I just used a screwdriver to GENTLY pry one clip out and push the wiring assembly away (up in my case) from the FSU just a hair. Same at the other end. Then it was a matter of pulling the thing off. I noticed that it is a VERY snug fit and even after the clips were not holding the wiring assembly in, it was still difficult to separate the two pieces. Of course, this was made worse by the cramped conditions.

I have 2002 X5 and am attempting to replace the final stage unit. Your instructions were so explicit w/diagrams even "I" felt I could do it.

My issue is I have gotten as far as "removing the plug w/the wires" which do not come with my hand pressure. Should it be this difficult or am I missing something. It is a tight space to work and my chubby fingers don't help. Any suggestions?

BTW, got the part from Amazon for $38.51

Many thnx!

Irvine, read my post, it may help:
http://www.bimmerfest.com/forums/sho...&postcount=538

Finished up this morning and its all good. Elvis addressed my main issue of "wiggling" the plug with wires (I missed that the first time I read the post). Also the cover under my glove box does have one screw that must be removed before yanking it out. It might have taken me a couple or three hours but am very happy to have that air blowing.

Originally Posted by Elvis530i

Does your A/C-heater blower seem like it's possessed? Does it quit working for no apparent reason, then come on again just as mysteriously? Does it run only at one speed no matter what the controls say? Does it keep running even when the car is off and the key is out of the ignition? Your problem is most likely a faulty final stage unit.

Based on what I've seen here and elsewhere, this is a chronic problem with the E39, but fortunately it's a relatively cheap and easy fix. There's a good DIY here, but since questions about it get posted here with regular frequency, I figured it would be a good idea to post one here too. Some of the photos in this post are very large because it's very helpful to see the details if you have no idea what's going on here.

BMW calls this thing the "final stage unit;" the parts guys call it a "blower motor resistor." I'm not sure what the reason for the different terminology is, but it's the same part. The PNs have changed a couple of times over the years, but as of the date of this posting, what you want is PN 64 11 6 923 204 and there's a diagram of the system here. As far as I can tell, the same part is used in all E39 models (but you may want to confirm this). Bavarian Autosport has them for about $70, but they're unfortunately available a lot of places, including the parts counter of your local dealership (I say "unfortunately" because it's a reflection of how often this thing fails).

For some reason, dealer service departments are notorious for not being able to recognize this issue, and may charge you for hundreds or thousands of dollars of unnecessary repairs without solving the problem. If you don't feel confident doing this yourself (i.e., you're the sort of person who is more likely to take an eye out with a screwdriver than a screw), at least bring them this information. Done properly, this is a 15-minute, ~$100 repair.

This is what you're replacing:


(Side view, with highlighter for scale)


(one end view)


(other end view)

The silver part of it is a heat sink. I'm not an electrical engineer, but I believe this thing allows the blower controls to change the speed of the blower by altering the current that passes through it. Inside is a bundle of resistors, and by sending the current through a different combination of leads, it creates the proper current to operate the blower at a desired speed. But resistors generate heat (thus the need for a heat sink), and over time, I suspect the constant heat up-cool down cycle degrades the resistors until they no longer produce the right current, and the controller can no longer send the right signals to the blower. Thus, the blower starts acting strangely despite what the controls are doing.

Now, I've read a lot of horror stories about how difficult this replacement can be, but I didn't find it that way at all. This is an extremely simple operation that took me less than 10 minutes. The hardest part was getting myself into a position where I could get at the faulty FSU.

All you need here is a Phillips screwdriver, a flashlight (the one in your glovebox will work fine) and understanding that you're working with electrical components, not mechanical ones. That means being mindful of how much force you're using. Nothing in this operation requires any great effort, so if you find yourself needing force things, you're doing something wrong.

The FSU is behind the dash in the passenger side footwell. You'll find it easier to work if you pull out the cover under the glovebox. It's not secured by anything, so just yank it out. The FSU is behind a fabric covered plastic panel on the left side:



You want to unscrew the screw (red circle), then slide the panel backward (see arrow), not out. It's also held in place by two metal clips that attach to the frame behind it:



Once you've got the panel out, lay on your back and look up at the space you've just exposed. The FSU is inside there.



Inside the space, you'll see a plug with 5 colored wires coming out of it. The FSU is the thing the plug is connected to, so you've got to get the plug out. The plug is held in place by two clips on the side, and you need to squeeze the clips to free it.



You may find the plug a bit difficult to get out; if so, just wiggle it back and forth until it comes free. Don't yank it out--you may break one of the wires loose, in which case you've just bought yourself an expensive and embarrassing trip to the dealer.

The FSU is itself held in place by another clip at the bottom. You need to push this clip down at the same time you're pulling the FSU out.


(note--plug is still in place in this photo, but take it out first. I didn't take a picture of the FSU with the plug out )

Again, if you're doing it right, you should not need to force anything. Once free of the clip, the FSU should slide out easily.

You may find all of this easier if you lay on your back in the footwell to get your bearings, then sit up straight, reach under the dash, and do it "by feel."

Now, surprise, surprise, the part you've just removed won't resemble the new one exactly, since as I mentioned, the PNs have changed a couple of times:



Hmm, could this be because the original version was defective?

Now just slide the new one in the spot the old one came out of. It should slide into place with a "snap" as the clip engages it.



New FSU in place. Note orientation--it will only go in one way. If you're having trouble getting it in, you've probably got it rotated 90 or 180 degrees out of alignment.

Replace the plug, then slide the panel back in the way it came out. Be sure to get both clips into their respective slots, or it will hang loose. Replace the screw.

If you've done everything right, your blower should operate normally now. If it's not, go back in and check the connections. If everything looks right but it still doesn't work, you may have other problems.

Got a question: I'm attempting this right now--are there any screws that hold the fsu in as there are two tabs on the FSU and I can't tell from your pics but on my new FSU part and looking at your pics it looks like there's a screw (loose? maybe?) holding one side of the old fsu in (the other one is obstructed by wiring so I can't tell. Another thing I'm having a bit of trouble with is it's so tight in there I can't hardly find the clip I'm supposed to press down on to remove the old one (let alone don't know if the old one's screwed in as well--it looks like I see one screww in there...) HELP!

Okay, so after tussling with it a bit I got it in but the blower motor still makes a steady wrrrrrrurllling sound. Hope it's not the blower motor going bad--I won't touch that--my mechanic can have at it and I'll but the parts. Word to the wise, if you have wide shoulders, be prepared to battle trying to get position well enought otackle the FSU. All in all worth it as I saved how much $$$$$???

Thanks Elvis!

Thank you very much for the post and great pics. My 540 was draining battery constantly and RAPIDLY but my blower was behaving NORMALLY when running. Pulled my fuses but it did not help. The drainage VARIED and when measuring it did not show up most of the time. A couple of quick note. The panel below glove box you have to pull towards the BACK of the CAR and it releases easily. I was able to disconnect the connector with the glove box still in place and my discharging battery was started behaving NORMALLY again!!!! It appears that the blower would kick in often with the car off. It started shortly after I kicked the heater to 90 when bleeding the coolant??? I have ordered an OEM Autohausaz just under $60, dealer wanted $150+

Update, part came in and is the newer style and works fine. FYI I did NOT remove the glovebox, only the tray under it. dont panic the newer unit goes in easier than the original comes out!!! you can push the tab down as you put it in place as I found that helpful. while the unit was unplugged the fan stayed at the last operating speed. Time for putting everything back was 5 - 10 minutes. Put side panel back in before tray under glove box (easier).

The posts here have been very helpful even though some are older.