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Old 03-23-2010, 01:07 AM   #1
bpiersma
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Radiator Fan strange behavior

So perhaps some experienced fanatics can help me with this one. The radiator fan (electronically controlled as I have a 99 328i manual) seems to not be working. My car runs a bit hot and I have replaced everything from the radiator to the thermostat to the pump. When idling, the car creeps up to hot until I speed up. I've let it get real hot and then checked the fan, and it is not on. I even checked at startup when it's supposed to turn on briefly to show it works...and it doesn't.
Here's the kicker...
If I put 12Volts from the battery directly to the terminals on the connector, I can get the motor to spin wildly. Does this make sense? Or do I have another issue I need to look into.
Thanks for any help, dudes.
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Old 03-23-2010, 01:40 AM   #2
hvirani
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You may have bad wiring. I'm uncertain if the DME is involved with the fan, or if its simply a temp sensor + relay deal.

Kpeng did a retrofit of his, I'm curious if he knows.
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Old 03-23-2010, 06:36 AM   #3
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Do you have any stored codes? Normally the ECU checks the fan motor when the car is started, it starts the fan at 20% of max speed, shuts it off and then checks the voltage OUTPUT of the motor to confirm the fan motor is still good. If it doesn't turn on it should set a code.
Have you checked the coolant sensor in the lower radiator hose? It is used by the ECU to control the fan.
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Old 03-23-2010, 10:14 AM   #4
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I did have one code...something like "Temp too low for closed circuit" but nothing about the fan. The fan does not go on at all when the car is started. Is it possible that the motor is ok, but that little box mounted on the shroud next to the fan is not? Is there a way to test that?
As far as the coolant sensor in the lower hose, that was replaced a year and a half ago.
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Old 03-23-2010, 11:25 AM   #5
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Looking at my Bentley manual it indicates a BMW code 10 "Engine coolant temperature out of predefined range" and lists either a faulty thermostat or cooling fan. I don't know if you can get just the power output final stage part or if you have to buy the whole fan. I didn't see it listed on RealOEM.com.

Temp too low for closed loop would make me check the thermostat, it may be stuck open if the code is recent. (clear it and see if it comes back)

Last edited by shanneba; 03-23-2010 at 11:26 AM. Reason: Added info for the temp too low code
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Old 03-23-2010, 07:23 PM   #6
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Where exactly did you apply the 12 volts to get the fan to spin? The connector on the top right side of the fan shroud should have 3 wires going into it. A ground, a permanent 12V supply, and a signal wire. If you look at the fan assembly you'll see a box mounted between where this connector and the fan motor itself. This is the final stage unit which is apparently the culprit in most fan failures. The DME sends a pulse-width modulated signal to the FSU to tell it what speed it should run the fan. Unfortunately the FSU isn't available as a separate item; you have to buy the entire fan assembly. If you're getting power at the connector, and applying 12v to the fan itself (directly to the motor, not to the leads going into the FSU) gets it running you probably have a bad FSU.

I'm facing a similar situation so I've been looking into this before I spend the cash on a new fan assembly. One lead I haven't been able to test yet is that the fan switch in the lower radiator hose can go bad and that will keep the fan from running at all, including the initial self-test.
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Old 03-23-2010, 08:03 PM   #7
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Quote:
Originally Posted by shanneba View Post
Do you have any stored codes? Normally the ECU checks the fan motor when the car is started, it starts the fan at 20% of max speed, shuts it off and then checks the voltage OUTPUT of the motor to confirm the fan motor is still good. If it doesn't turn on it should set a code.
Have you checked the coolant sensor in the lower radiator hose? It is used by the ECU to control the fan.
Does the ECU always kick the fan on at start up? Mine doesn't. No codes and no overheating at all. Thx, Chas
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Old 03-23-2010, 10:20 PM   #8
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Tangent,
I had the same thought about the fan motor being ok and the FSU being bad, so I applied the 12 volts to the connector. That way, I could tell if the FSU was allowing the power through to the motor. The motor worked right away the blade was whirling. I'm trying to track down an ohms chart to see what that temp sensor in the lower radiator hose resistance should be, but since it is only a year and a half old, I'm not thinking it is a suspect. Again, back to square one. Any other thoughts?

Chas, According to my Bentley, it is supposed to click on briefly at 20% of speed right on startup. Mine is a 99 manual, though, so there could be a difference.
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Old 03-24-2010, 12:42 AM   #9
bpiersma
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Update:
If I put 12 volts to the fan connector in reverse polarity, the fan spins. If I put the 12 volts on in the same configuration as it gets from the connector, no movement. What does this tell me?
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Old 03-24-2010, 02:49 PM   #10
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Weird... Does the fan spin the right direction when you apply power backwards from what it's getting when plugged in?
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Old 03-25-2010, 12:06 AM   #11
bpiersma
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Quote:
Originally Posted by Tangent_ View Post
Weird... Does the fan spin the right direction when you apply power backwards from what it's getting when plugged in?
Yes. It sends air back toward the engine. Can't figure out if it is bypassing a faulty sender or what. Also, the temperature sensor in the lower hose measures 2000 ohms at cold.
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Old 03-25-2010, 10:06 AM   #12
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I am having the exact same problem ie: temp creeps up and unless i can get a good airflow going(no traffic) i will overheat and when i pull over to check it NO FAN .

later the same day or the next day everything is fine and while driving to/from work i will hear the fan running as normal.

this happened yesterday after work and NO FAN so i let it cool off then as i went home it went straight bak to the middle and when i was in the driveway the fan was running really slow......only the day before as i parked at my work the fan was running furiously ....so i am perplexed.

from the previous posts it seems as if the temp sensor in the lower radiator hose is what turns the fan on??? what is this FSU?? anyway thanks for the help...

doug hunt
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Old 03-25-2010, 12:16 PM   #13
bpiersma
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The FSU is the little black box with the plastic cover on it, attached to the fan shroud assembly (I assume you have a manual transmission). It is responsible for turning the fan on or off based on what the computer tells it. The computer takes information from the temp sensor and other things to determine what signal to send to the FSU. So, if your FSU is fried (as I've heard they do far too often), then you could get sporadic fan functionality. What I did was test the resistance on my temp sensor and found that it was 2000 ohms. Then I shorted the wire that goes to the temp sensor with the thought that it will tell the computer that the fluid is really hot, and trigger the fan. But, my fan did not move. So, I have concluded that indeed my fan is fried. I just ordered one and I'll post my results next week.
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Old 03-25-2010, 01:07 PM   #14
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Thankyou bpiersma, (yes it is a 5 speed) i am going to try the temp sensor test as you have described and then move forward........i had a expansion tank failure last summer in august, but unfortunately was too short on funds to replace "everything" at that time. Now i check coolant level fanatacally but i am still getting this crazy intermittant NO FAN overtemp.

thanks again i will be checking here and i will post my findings as well
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Old 03-25-2010, 01:09 PM   #15
nvoges
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My fan doesn't want to shut off. Do you this could the same problem I'm experiencing?
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Old 03-25-2010, 01:27 PM   #16
Stingray230sx
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well, i am leaning towards the FSU as the real problem...but i havent checked my temp sensor or tried to short it to see if my fan comes on.

i know that in the past i was always hearing the fans run, especially after a trip from work to home in 5 oclock traffic.....i am thinking that maybe when my expansion tank popped, it contaminated the FSU box and now i have a intermittant fan problem....i hope its my temp sensor as that is 31.00 from the dealer and a new fan is 477.38 sheesh!!!!

will try to test the temp sensor this evening after work........


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Old 03-25-2010, 01:58 PM   #17
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The fan is 253 from Pelican Parts. Still not cheap, but better than the dealership at least...

Quote:
Yes. It sends air back toward the engine. Can't figure out if it is bypassing a faulty sender or what.
Which connector are you applying 12V to again? Not the one the yellow arrow is pointing at in the pic right? That should be getting 12v at all times anyway...

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Old 03-25-2010, 02:39 PM   #18
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thanks tangent, yea thats a much bettr price i cant check many sites at work, i can get to this forum,and the pelican forum but when i try to get to the parts section i am blocked, cant get to realoem for part numbers either, though my coworkers puter is strangely unblocked today and i got a few p/n's to call the local dealer. if its within 20 bucks i will use the local dealer cause of shipping and wait time etc, though usually the dealer cuts me a break, even though his fone quotes are list the last time i bought stuff it was less than list (about the same as tischer was i beleive).

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Old 03-25-2010, 05:56 PM   #19
bpiersma
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Tangent,
Yes, that yellow arrow points to the connector I applied the 12 volts to. I realize that it gets 12 volts all the time, and that's why I tested it. Of course, it did not spin when I applied the + and - in the same configuration as it gets from the connector (and I did test the connector to make sure it was supplying a constant 12 volts, and it is), but when i reverse them, that's when it spins. Either way, there are NO circumstances under which I can get the fan, when installed correctly, to turn on normally (without applying the voltage directly in reverse polarity).
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Old 03-25-2010, 06:03 PM   #20
bpiersma
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Stingray,
I ordered from BMWPartsWeb.com and it was free shipping...$252. Also, this whole thing started for me when my tank blew two summers ago. My theory is that my fan was shot already and not keeping the engine cool enough, which led to the tank exploding (I had been having intermittent overheating when driving in traffic on hot days). When I put in a new tank, it was strong enough to endure the increased pressure and temperature until...my radiator cracked. Once I replaced that (last week), I discovered that my fan has not been coming on at all. Also, I have ruled out the temperature sensor because 1) i just replaced it and 2) when I short out the connector wire, the fan still does not go on as it should.
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