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

Originally Posted by ecool

I think I might have the same problem. My blower sounds like it is pulsating when the heat is on, blows hard for a second then soft and then hard again, until the car heats up. I also had a dead battery the other day after the car sat for three days. The battery was just replaced in September. Do these symtons sound familiar to anyone who has replaced the FSU?

Those are the symptoms that I had, well the dead batt part. I went through 2 batteries.

Devroots.....did the FSU fix the problem?

Originally Posted by ecool

Devroots.....did the FSU fix the problem?

It most certainly did

Great pics. I am on my second E39. on both this item has blown out leaving me without AC.

just did this in the parking lot.

GBP 52 + VAT .. 20 minutes. The dealer was quoting 45 minutes of repair time and even mentioned the car may need to be recoded for the new part. .... i mention to him that it is just a resistor ... he replied you are right ....


usefull post.

This directions are great. I called my dealer and he asked for $ 400 to replace this part. I purchased it online for 68 and ended up replacing it in less than 30 mins.
Thank you all

Can you guys help me out! I cant seem to be able to pull FSU out, i cannot manage to push on the part and pull on the same time, no room for my fingers.. is there an easier way to pull it ..
thanks u

I need help guys, i cant seem to pull the FSU out and pushing on that piece at the same time> anyone have easier way. I TRIED everything.. my fingers all all bloody and broosed.. its seems like it doesnt want to come out!!
thanks

Elvis thanks a bunch. These directions are the best especially since they include pics.

Originally Posted by stas

I need help guys, i cant seem to pull the FSU out and pushing on that piece at the same time> anyone have easier way. I TRIED everything.. my fingers all all bloody and broosed.. its seems like it doesnt want to come out!!
thanks

I shed some blood changing my FSU too. It really helped when I took the plastic panel off that is under the glove box. After that came off I was done in ten minutes. Had some problems getting the new FSU to snap into place but it finally went and now I have no heater problems at all.

The instructions for replacing the Blower Resistor / Final Stage Unit were perfect. Job took 10 minutes and saved bundles of money. I'm sure the shop would have quoted for removing the dash etc. However, the spaces are tight, and you need to be careful not to pull wires or force things. Best to park the car with bright sunlight streaming thru the passenger side door, and augment with the best shop light you can find. After removing the plug it's probably best to tie the wiring loom carefully up and out of harm's way, so that you have a freer hand, as there's only space for a few fingers. When re-installing the FSU, the aluminum rods seem to catch on the side of the opening, so it may be necessary to remove and try again. It took 3 - 4 tries until the unit seated on its foam gasket and clicked home. Thanks!!!

Elvis thanks a bunch. These directions are the best especially since they include picstures ,took me a while to find the information but it was worth it,it save me some money...

thanks for the great post about the resistor,it was driving me crazy...bought the part and installed myself

Right after my very first bimmerfest brake job, the interior fan stopped working altogether. I was told in that brake DIY to check over here regarding the cause (http://www.bimmerfest.com/forums/sho...=1#post3124559).

After reading this post, I see the fan motor problem could be the porcupine FSU or it could be the fuses apparently hidden deeply behind the glovebox.

I'll definitely check the glovebox fuses; but, before I go out and get a FSU, may I ask if there is a diagnostic procedure for determining why a fan suddenly stops working?

Or, is replacing the fuses and FSU the only diagnostic that is available?

I just wanted to say thanks a lot for posting this. I'm sure it saved us a bunch of money. I just ordered also the part for about $70 at bav auto, followed your instructions and it's done. My A/C is working again

Thanks to you it took me about 25 minutes and it's all done!

Thanks for the great writeup



Thanks again!

Originally Posted by texbid

Great pics. I am on my second E39. on both this item has blown out leaving me without AC.

just did this in the parking lot.

GBP 52 + VAT .. 20 minutes. The dealer was quoting 45 minutes of repair time and even mentioned the car may need to be recoded for the new part. .... i mention to him that it is just a resistor ... he replied you are right ....


usefull post.

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.

These instructions were awesome.Thanks Elvis! this is the first part I replaced on my BMW and it took me 10 minutes based on your instructions. Cool.

For all those folks who replaced their FSU, besides the obvious physical difference ...
- What was the electrical difference between the old and new FSU?

Rather than run out and replace hundred-dollar parts without even knowing, ahead of time, if they're actually good or bad, would it not be prudent to first test pin-to-pin resistance (or something electrical) before willy nilly putting new parts in to replace the old? Luckily, the FSU seems eminently testable, if it's indeed just a bank of heat-sunk resistors ... a simple ohm meter might work fine if an open or short or extreme change in resistance value is the actual cause of the apparently common problem ...

- Do we have a pin-to-pin spec or wiring diagram for the FSU?

If, in the unlikely event, nobody has already done this, would the next person (who reads this after buying a new FSU) please report back to us the delta between an old and a new FSU with respect to pin-to-pin electrical values?

Since I started this thread, I've never heard of anyone having come across such data, so it would need to be gathered.

I suppose it would be a good thing to add to the thread, but in practice, this is such a common problem with such obvious and distinctive symptoms, that replacing the FSU doesn't really qualify as "willy-nilly" in my book.

That said, I would be interested in seeing exactly what the differences are between a new and faulty units.

I would be interested in seeing exactly what the differences are between a new and faulty units.

Hi Elvis,
I understand that almost everyone in this thread and elsewhere replaced their FSU whenever anything went wrong, e.g., http://www.540i6.com/finalstagereplacement.html

However, some replaced the FSU and the problems persisted, e.g., http://www.dtmpower.net/forum/e36-3-...stor-help.html

Some said it was the blower motor itself; others implicated the control unit; while none implicated the two sensors in the circuit.

So, it's, uh, well, it's as clear as not very clear. Seems to me, the FSU can't hurt, and, it doesn't cost a lot but, it just goes against my grain to replace without testing first. If I have to buy equipment (within reason) to test the thing, well then, so be it.

The question becomes what to test once the FSU is in our hands. Do we have a WIRING DIAGRAM?
Oh well ... If I end up getting a new FSU (I'll wait to see if it goes out AGAIN), you can rest assured I'll ohmmeter it while both are in my hands!

If the FSU is merely a bank of resistors, we'll see a short or open; if it's a bunch of power transistors, I'm not sure what we'll see ... as we might have to bias the transistors to get it to show it's mettle ... either way ... let's begin to gather the data starting with the very next person who has a bad and good BMW FSU and/or blower motor in their hands!!!!!

Thanks,
Donna

Here, by the way, is what a BMW blower motor looks like ...

Hello all,
I have a 525TDS-1996.
Symptoms: Battery goes flat so replaced it with a new one but still the same issue.
My temperature needle sometimes goes up to quarter mark and other times to two thirds whereas it used to be at halfway point all the time.
I have not seen any problems with my blower unit as many have reported on here.

Please advise if its FSU that I need to replace or need to investigate further?

Thanks in advance for any help or tips.

ps. My first ever post on this forum.

Doesn't sound like the FSU, if you're not seeing blower issues.

I finally started to see the classic blower symptoms so I went ahead and swapped out the FSU unit following Elvis's excellent detailed instructions. The issue has now been resolved.

Thanks for your help and good work Elvis.

FSU costs £63 incl VAT from BMW dealer.

Just want to say big thanks.Recently had the same problem and my mechanic sent me to a main dealer.Lucky me..found your post and fixed by my self..New part coust me £63 pounds..Thank You!

Originally Posted by bluebee

The question becomes what to test once the FSU is in our hands. Do we have a WIRING DIAGRAM?
Oh well ... If I end up getting a new FSU (I'll wait to see if it goes out AGAIN), you can rest assured I'll ohmmeter it while both are in my hands!

If the FSU is merely a bank of resistors, we'll see a short or open; if it's a bunch of power transistors, I'm not sure what we'll see ... as we might have to bias the transistors to get it to show it's mettle ... either way ... let's begin to gather the data starting with the very next person who has a bad and good BMW FSU and/or blower motor in their hands!!!!!

Donna,

Here's the FSU wiring diagram from Bentley:


Unfortunately, it is full of transistors, and these intermittent problems are tough to troubleshoot.

F76 - Fuse 76
15 - Ignition power (RUN & START)
30 - Batt positive (+)
31 - Batt negative/gnd (-)

Originally Posted by riro424

Donna,

Here's the FSU wiring diagram from Bentley:

Unfortunately, it is full of transistors, and these intermittent problems are tough to troubleshoot.

F76 - Fuse 76
15 - Ignition power (RUN & START)
30 - Batt positive (+)
31 - Batt negative/gnd (-)

Good to know anyway.

Good to know anyway.

I agree! Sorry I didn't chime in sooner. My FSU seemed to have "fixed" itself (except for the early morning wheezing) so I didn't pursue this further.

But I did send your BMW FSU wiring diagram to an electrical engineer friend in the silicon valley who wrote back the following that might help the next DIY.

> Does this electrical BMW FSU thingey look easy to debug?

Well, if you have access to the wires in the car, I guess it shouldn't be too bad.
You can see that the terminals are:
1,5) blower
2) +12
3) control input (in spite of being drawn as the collector of a bipolar transistor!)
4) ground

So I would:
A) spray WD40 on the contacts
B) check terminal 2 for voltage
C) put a two channel scope on terminals 3 and 1, and then 3 and 5

Now the question is, is that much effort worth more than
the $100 or so to just replace the unit? Consider your
options. Either the unit is bad, so replacing it is required.
Or, the control unit is bad. That's going to cost a bundle.
So maybe spending $100 is a reasonable thing to do.