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

1M views 696 replies 440 participants last post by  rakitha92.p 
#1 ·
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 :rolleyes: )

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? :rolleyes: :dunno: :mad:

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.
 
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#28 ·
I don't think a bad FSU will cause the whole control unit to die. Sounds like something else. But, I'd ask the mechanic when you take it in to check.
 
#29 ·
Fsr

You guys rock! Thanks for all of your info. I replaced the Final Stage Resistor in about 15 minutes on my X5 and everything (AC / Heater) works like new. The tip about using needle nose pliers to squeeze the tabs and wiggle the electrical connector out worked great. I never knew that there was even a 12 volt/cigarette plug under the dash until now.

I've now replaced the FSR and two window regulators thanks to your tips/advice. Sure beats paying big bucks at the BMW stealerships.
 
#32 ·
wish I'd read your post first!

The heater control switch on my 2000 528I suddenly doing exactly what your's did, run at maximum no matter where the fan switch was set.
Stupid me, I took it to the dealer before checking Bimmerfest postings. I don't know if your marvellously detailed photos and descriptions would have helped me with my problem but as I've complained to BMW, why should they keep installing a switch that can't last 30,000 miles of benign care? So now I'm out nearly $300 for replacing it.
 
#33 ·
quick tip on getting the fsu out

First of all, thanks to you elvis for writing this up and posting the pictures. As a quick tip, i just finished this procedure on my 97 540i and had some trouble figuring out how to push down on the main clip and pull out the fsu at the same time because i could only fit one hand up into the crevice. However, I noticed that the particular old unit in my car actually has a very small metal "handle" below the socket where the wire harness attaches. I found a very small "plasti-cuff" (one of those one-piece plastic things that you see the cops using for handcuffs occassionally where one end zips through an enclosure on the other end) in my toolbox and was able to hook it up to the handle with just one hand (a small allen wrench might work also??). The plasti-cuff now gave me a 4-inch handle to pull with my left hand while my right hand could sqeeze into the opening to depress the clip holding the fsu into place. It came out easily this way and I was finished shortly thereafter.

Thanks again,
David:thumbup:
 
#34 ·
Many Many Thanks to Elvis and all the other helpful tip posters for the FSR repair.

I think I may need to replace the FSR but sounds like, from other postings, that I need to check fuses first. I'm a super novice/amateur BMW chick so please forgive me for needing to ask which fuse(s) to check. I'll check the manual as well, but I want to make sure I check the one or ones related to the FSR (or climate control) if that makes a difference. Any advice? Thanks

2003 BMW 530i
 
#35 ·
There's a fuse that controls the blower motor, but it's in a godawful difficult place to get at. It's such a pain in the ass to find and get out that I almost think it's easier to replace the FSR first (though not cheaper).

The fuse is in a little two-fuse box up behind the glove box. You have to pull out the plastic cover under the glove box, open the glove box, then reach around behind it (you won't see it looking through the glove box). It's up about as far as you can possibly reach, and it's hard to even see it even if you lay on your back in the footwell and look up with a flashlight. I believe it's the rear fuse in this box (i.e., the one closest to you while pulling it out). Note that the fuses are upright in this box, which means you have to push/pull the fuse up even further to get it out, rather than pulling it down.

90%+ of the time, though, the problem is the FSR. If you're getting anything at all out of the vents, it's likely not the fuse.
 
#36 · (Edited)
ELVIS530i, this seems like a great post....sounds exactly like the problem i have....heaters never seem to switch on! and when i'm driving above 25mph i can feel little bit of air coming out of them...the faster i drive the more air seems to come out...thats maybe just the wind making the fans turn....but yeh then come the good times when he heaters start working, FOR A BIT...but if i;v been driving for a long time, they seem to come on abit more...but still seem possessed...

i drive a 1999 BMW 318Ci...anybody got any pics of what it looks like on a 318Ci??? hope its not too difficult/different....the dealer did say it was a long winded process....
 
#38 · (Edited)
Many thanks for sharing this information with us.

I own a 2001 530i with 63K miles. A few months ago, I noticed strange behavior with the A/C and heater. Sometimes they work and sometimes they don't. When they work, I can't control the speed of the fan (but I was able to turn off the unit). The dealer (Stevens Creek BMW) asked $200 to replace a "controller" (they said if that does not fix the problem, they will replace the whole unit for $1,000+). I declined the dealer's offer to replace the controller and searched online about known problems with the A/C and heater - and I came across your article. After looking at your article and the photos, I was convinced that the problem will be resolved by replacing the FSU unit. So, per "domiguy" suggestion, I ordered the FSU unit from AutoHaus for $63, and replaced the unit per your instructions. Now I am able to control the fan.

While replacing the FSU, I found it difficult removing the wire and sliding the old FSU out, because of a cover right below the glove compartment. In your photo that says "follow the wires... FSU up there", I suggest you also show how to remove the cover below the glove compartment so that you have more room to work. I was not able to remove the cover, so I struggled to replace the unit.

Overall, your instructions are great. Many thanks once again.

Cheers!
 
#39 ·
While replacing the FSU, I found it difficult removing the wire and sliding the old FSU out, because of a cover right below the glove compartment. In your photo that says "follow the wires... FSU up there", I suggest you also show how to remove the cover below the glove compartment so that you have more room to work. I was not able to remove the cover, so I struggled to replace the unit.
Here's the cover, looking up from the floor at the underside of the glove box:



Just grab the front of it and yank it straight back. It should come right out.



:thumbup:
 
#40 ·
Elvis; YOU DA MAN BAYBEE!!!!!!

Elvis, just had to Thank You so much for your fantastic post on the FSU issue. I bought the part from BAVAUTO for $63 vs. $120 from the local dealer. BAVAUTO is my favorite place to get my Bimmer parts. Great service, quick delivery and Free Delivery to boot!

Anywhoo, I took my Grey Ghost to a local BMW mechanic, he wanted $80 for diagnosis. I waited and found your thread while searching the Web. I had posted on other Bimmer sites with no luck...

Was in and out of my car in less than 20 minutes!! Is the original part defective??? It resembles the cell phone from the early 80's compared to the new one!!

Thanks Elvis, you saved me and other some major bucks. UDAMAN!!
 
#41 ·
Thanks for the how-to.
my wife called my on the way home from school (teacher) and she said the heat wasn't working (2002 X5). i did a quick search on another forum, and it pointed me over here. so off to the stealership, $96 (OTD) & a little later, it was all fixed :)
if it wasn't winter, i would've ordered the part.

at least it was a real easy fixed compared to our Range Rover.
 
#42 ·
Thankyou so much for this post!
After 4 occasions this weekend where my battery had insufficient charge to start my e39, a quick search on bimmerfest gave me the solution.
£59.00 incl vat for the fsr, or hedgehog as my stealership referred to it as, and then reading ALL of the replies to your post, after I couldn't find the thing in the car (I'm a right hand drive and it's on the drivers side!!!) I'm all fixed

Many thanks

Ian
'02 520i
 
#291 ·
Hi Ian

I was having the same problem with my 2002 E39. After cheching the forums i found out about the FSR and replaced it , and everything is working perfect. However i did have some concerns about how hot the resistor becomes when the heating is turned on which did alarm me, i mean it gets so hot it would burn your hand, did you notice this with yours ? can anybody tell me if this is normal.

Homer J
 
#292 · (Edited)
it gets so hot it would burn your hand ... can anybody tell me if this is normal.
Does anyone actually know how this FSU/FSR basically works?
And how to test if it's bad? (other than just replacing it w/o thinking ... which is what most of us did)

The best I can glean from the wiring diagrams and threads where people took it apart and actually fixed the bad solder connections is the following (perhaps incorrect) summary.

Can someone take this FSU-test-procedure from here and explain how this FSR actually works & how to test it?

How the fsu is wired:
Pin 1 = (bottom left) to wiring diagram #31; then to battery negative/ground (-)
Pin 2 = (bottom middle) to fuse F76 (40 amp); then to #30, then to battery positive (+)
Pin 3 = (bottom right) input to fsu from heat/ac module, #15
Pin 4 = (top left) output power to the blower motor? (speed 1?)
Pin 5 = (top right) output power to the blower motor (speed 2?), #I5, Ignition power (RUN & START)

Test procedure, from this thread ...
Pins 1 (SW/GN wire) and (5 RT/GN wire) are the negative and positive to the blower motor (right???)
- If you ground pin 1 and apply 12 volts to pin 5, the blower motor should operate; otherwise the blower motor is bad.

- If you test resistance between pin 1 and the metal chassis fins, you should get zero ohms (right???)

- Test if pin 2 (the fuse 76 circuit) has 12 V when the HVAC button is switched on.

 
#43 ·
Elvis 530, thank you for saving me hundreds....hopefully. I went to my local mechanic and they quoted a ridiculous price saying that it was something difficult to get to. They even mentioned that they'd be replacing the fan motor. I just ordered the resistor from Autohaus so I'll keep you posted with the results following the replacement. Hopefully the motor isn't the problem.

Also, would this problem cause a parasitic draw from the battery? I had to have my 530 jump started on Sat. night, replaced the battery on Sun. only to find that the brand new Duralast 49DL was dead Tues. morning. I've got the car at the shop now and they're searching for what's causing the draw. I believe he stated that there were nearly 5 amps of draw. I took it in yesterday afternoon and they're still searching. I'm out roughly $500 for the investigation work and am wondering if any of you may have experienced something similar.

Help ASAP. Thanks.
 
#44 ·
Also, would this problem cause a parasitic draw from the battery?
Yes, that can happen. Sometimes the fan will keep running even after the car is off. It didn't happen to me, but I've heard of it happening to others.
 
#45 ·
Thanks for this info, its nice to see someone put all this good info together for other peeps. I just had to replace this relay on my 5 this last week (not knowing about this article) and I was skeptical of the advice given to me by a friend of mine with a 3, but he was right and 80 dollars later I have working climate control again! :thumbup:
 
#47 ·
Hi there, my airco stopped working a few days ago. I can hit the airco button and it lights up. But the airflow from the vents doesn't change. So I started to search the net and came upon this post about the FSU and thought maybe i've the same problem because sometimes when i get into my car i can hear a little vent blowing behind the climate control unit (while the key isn't in the ignition). Not very hard though and always at the same speed. But it's not always there so maybe it's the same thing? Or should i bring it to a dealer to get the diagnose first?

Thanx Braz
 
#50 ·
Okay, the black panel pulls straight out, it's got two white snap rails on the back, just tug it.

Man, I've got it done, but you almost have to be a contorsionist at my height to do this! Everyone wants to be tall, but when it come to fitting in tight spots, holy moly! It's done :)
 
#51 ·
No kidding. As I said, I found it easier to sit up straight and just do it by feel instead of trying to twist my spine into a pretzel shape. :angel:
 
#52 ·
FSU replacement

Elvis,
Your information regarding my 2001 BMW 525i fan problem was right on. I had suspected some problem with the AC/Heater fan. The final problem occurred when I had recurring dead battery problems and noted that the fan motor had a mind of it's own and was turning on without the key in the ignition :cry: After researching on the internet and finding your post, I new the FSU was likely the problem. I purchased a new unit, followed your instructions/pics and ----- problem solved :) Thanks
 
#56 · (Edited)
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.
.
this thread only refers to possessed blower, meaning that the a/c still blows some air.
My blower motor doesnt seem to work at all. I switch my a/c on and I can hear the compressor kick in but no air. i continue to turn the fan speed up to max and still no air. Does replacing the FSU fix the blower problem or is my blower out? I wanted to replace the FSU yesterday but i had a feeling it was the fan. I took my car into an independent BMW repair shop and they supposedly tried replacing the FSU and the fan didn't run(is he blowing smoke up my a$$?). anyhow, he quoted me $700 to replace the blower fan motor which costs about $375.

first symptoms, i heard clicking sounds under the dash. I turned off the radio and it was still making that sound so i turned off the a/c. I noticed the sound went away, i than turned on the a/c again and it came back. after turning on and off the a/c the blower decided to crap out. So the blower right now is not working at all. I would like to know what yall think this could be. Thanks for all the advice and help.

Elvis- Great post, very detailed! Keep up the good work.:thumbup:
 
#63 ·
Hey there...I have a 90 535i that has a similar problem to cheweez. I can hear my AC compressor kick on, but the blower doesn't blow at all.....well sometimes it will first thing in the morning, but only for a few minutes. I pulled the FSU (My car has the "sword" style) out and looked at it...definitely looks a bit crusty. That's a $200 part for my car. I'm just wondering if I should start with that, or if I do some other diagnostics first? I pulled the fuse out and looked at it, but how can you tell if those box-like fuses are blown? And I doubt it is blown if the blower does kick on every so often.

Basically what I'm trying to get at...do you guys feel pretty strongly that it's the FSU? I'm fine with buying it...hell the dealer was going to charge me $800 to fix it, and they were talking about getting behind the dash to check on all the wiring to find a short in the system.
 
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