Bimmerfest - BMW Forums - View Single Post - Replacing the final stage unit/blower motor resistor (E39)
View Single Post
Old 08-03-2013, 08:11 PM
DSTedeschi DSTedeschi is offline
Registered User
Location: North Texas
Join Date: Aug 2013
Posts: 1
Mein Auto: M3 and 5 Series Touring
After spending a lot of time reading the excellent postings in this thread and thanks to BlueBee for the links my fan is blowing cold air. A big deal during summer in Texas.

I would like to summarize some things that would help those in the future.

First if you fan is not running or running erratic the FSU is suspect, not guilty.

Remove the FSU per the wonderful instructions presented here. Then the next thing to do is check the resistance of each pin. This requires a Volt Ohm meter. A fact of life is if you are going to do DIY repairs a good Volt Ohm meter is required period. A surgeon does not work with a straight razor, nor can the Mechanic work with a cheap meter or without one. Invest a few dollars in a good one. I have owned my Fluke for 15 years and I did pay around $200 for it. An investment that has pay for it self many times.

There are drawings in this tread that has resistance values of each of the 5 pins. BlueBee had some links also. Just set your Ohm Meter to resistance and have one probe touch the pin and the other to the longer aluminum pins in the back of the FSU.

In my case two of the pins where open, no resistance at all. BINGO I thought, it is the FSU.

Being an older Engineer I did wanted to ensure that the fan was working. I have been down this path too many times with my Engineers during lab check out, not checking everything.

To do this you need to ground Pin One on the plug connector. And take power from plug two to plug five. Be very careful the power at plug two has a 40 amp fuse. When I did this fan fired up and I was assured the the FSU was the cause. Here is the diagram of the plug. This was something that was missing in everything I looked at and is important to validated that you have a good fan.

5 (Fan High Speed)----------------4

3----------------------2 (Fused 40A Power)---------------1 (Ground)

I even soldered ends (small brass tubes) to wires so that they would fit into the plug and an alligator clip on one of the wires end to attach to a ground. I used bracket near the transmission tunnel around the carpet as the ground attach point. At one point I used paper clips and the one at the plug 2 shorted, melted and then caught the print outs I had laying on the carpet on fire. Lucky nothing was damaged and nothing burnt. LUCKY!!! and that is why I soldered ends to real copper wires.

I purchased a new FSU at the dealership and did so because Autobahn in Fort Worth gives a BMWCCA discount and when I need something I don't mind paying a little more for a part.

As of this writing the car is blowing nice cool air and 100 degrees in Texas is not an issue.

Note: if you are having issue with paying out $200 for a meter, what would be the cost just to have someone, dealership or independent, figure out what was wrong?
Reply With Quote