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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 12-15-2011, 08:00 PM
windsoftime windsoftime is offline
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Mein Auto: 325ci convertable
fsu testing

I have a 2002 325ci convertable and the fan has stopped working. is there a way to test the final stage unit?
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  #2  
Old 12-15-2011, 08:09 PM
Steve530 Steve530 is offline
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I've never seen a test to determine if the FSU has failed, only symptoms that indicate that the FSU is malfunctioning.
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  #3  
Old 12-15-2011, 09:59 PM
windsoftime windsoftime is offline
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Mein Auto: 325ci convertable
fsu

my fan motor totally quit so I'm guessing it's the fsu as the fuses seem to be ok and rarely the the fan motor pack it in. I just wanted a test before ordering a replacement.
thanks for the feed back
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  #4  
Old 12-16-2011, 04:22 AM
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Fudman Fudman is offline
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Most folks just replace it. Just get an OEM FSU or you'll be doing again soon!
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  #5  
Old 12-16-2011, 04:30 AM
JimLev JimLev is offline
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You can test it, but it's most likely bad if all of the fuses are good and the HVAC panel is working
FSU connections:
Pin 1 to blower motor (or a test load, light bulb)
Pin 2 to 12 volts
Pin 3 to 0-5 VDC (this is the speed control input from the HVAC panel)
Pin 4 to ground
Pin 5 to blower motor (or a test load, light bulb)

Vary the 0-5 VDC and the motor (or lamp) will follow if the FSU is good.

Don't buy one from ebay, they are mostly junk and don't last, get an OEM FSU.

Last edited by JimLev; 12-16-2011 at 04:33 AM.
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  #6  
Old 12-16-2011, 10:39 AM
edjack edjack is offline
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There are at least two failure modes: erratic, uncontrollable speed fluctuations; no blower function.

A faulty FSU can also drain the battery.
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  #7  
Old 12-16-2011, 12:46 PM
Turbo_525 Turbo_525 is offline
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Mine drained the batter. I would just get a replacement from your dealer and take the ~30 minuites it takes. Search for the FSU thread - good info there!
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  #8  
Old 12-17-2011, 11:00 AM
jygesq jygesq is offline
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Quote:
Originally Posted by windsoftime View Post
I have a 2002 325ci convertable and the fan has stopped working. is there a way to test the final stage unit?
they all do that. FSU . good write up.
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  #9  
Old 12-18-2011, 01:16 AM
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bluebee bluebee is offline
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Mein Auto: 02 BMW 525i M54 automatic
Quote:
Originally Posted by JimLev View Post
You can test it
That's nice information.

When I search for "fsu" in the bestlinks, I find:
- Understanding and TESTING the Final Stage Unit (FSU/FSR)

So I'll add your information to that set so that others can find it more easily in the future.

See also:
- What is the canonical thread on the BMW E39 FSU/FSR/Blower Motor Resistor (1) and what is the right brand FSR to purchase (1) (2) when your interior heating & air conditioning HVAC/IHKA blower motor goes haywire (1) (2) (3) (4) (5) (6) (7) (8) & how to test the FSU (1) (2) (3) & how to repair your own final stage resistor including an autopsy & wiring diagram schematic (1) (2) and why a bad final stage unit will cause the battery to drain overnight (1) (2) (3) & how to isolate and replace the E39 blower motor (1) (2) (3) (4) (5) & how not to replace the FSU (1)

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  #10  
Old 12-18-2011, 03:49 AM
JimLev JimLev is offline
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Just reading the resistances won't tell you a lot.
Different ohm meters use different battery voltages which will effect the readings.
Once defective transistors are powered up they start drifting, shorting out, etc.
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