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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 07-02-2012, 04:11 AM   #1
devlspawn
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How to Trouble Shoot (test) Radiator Electric Fan

I'm posting this because I searched every thread I could find on the subject of trying to figure out which component is the problem when your electric fan isn't working and there seemed to be a lack of information or what information was there was not correct.

I discovered my electric fan was not working on my 2000 328i (Manual). I wanted to test which part of the system wasn't working before I dropped $300 on a new fan. Here is what I found:

One main thing to point out is the Manual version of the car has a single electric fan on the engine side of the radiator. The automatic has an electric fan on the grill side of the radiator plus a mechanic belt driven fan on the front of the motor. The one on the grill side should be nearly identical in troubleshooting to the electric fan on the manual.

The fan is controlled by the computer (DME). The plug that goes into it has 3 wires (this is the plug on the left side when standing in front of the car facing the fan, the device mounted to the top of the fan is an air particle sensor and has no bearing on the cooling system). The two large wires are for power and ground, they are always live even when the car is off. They are hooked to the 50 AMP fuse in the glove box #36. The third wire is to control the fan speed and comes directly from the DME, there is no other fuse or relay in between. This wire carries a Pulse Width Modulation (PWM) signal.

The wires from this connector run to a box on the engine side of the fan (which the manual calls an "output final stage") and two wires go from there to the fan motor.

The car is supposed to run the fan for 20 seconds when you first turn the car on, then check to see if it is spinning, if the fan is not spinning the computer should set a code. I had no codes set on mine though.

The fan is almost always on at some speed if you have the A/C on, so perform tests with the A/C running.

The inputs the computer uses to decide how fast to spin the fan are:
Radiator outlet temperature
Catalyst temperature (calculated
temperature)
Vehicle speed
Battery voltage
A/C pressure (calculated pressure)

To troubleshoot:
  • check computer for any set codes
  • unplug the fan connector and test for voltage on the two large wires.
  • If there is no power check the fuse in the glove box
  • If you have an oscilloscope you can use that to easily determine if you have a PWM signal on the wire from the DME, if not continue reading
  • Measure voltage from PWM wire to ground
  • I assumed my multimeter would give me the average voltage from a PWM signal but apparently not. I measured about .03 volts almost always when the car and A/C were on. I'll let the electronics buffs tell me why my assumption was incorrect.
  • If your multimeter has a frequency option test the frequency on the PWM wire.
  • On mine I measured 190hz during the first 20 seconds and 240hz after that. Many posts have said the correct range is 10-100hz, but unless my multimeter is very far off that is not the case
  • If readings on all those are ok then it's either the output final stage or the fan motor itself. You can check the motor by pulling out the fan and applying 12V directly to the motor (there is a small square plastic cap in the middle of the fan you can pop off for easy access).

In my case the motor would spin when powered so I figured it had to be the "output final stage". Unfortunately they don't sell just that part, you have to buy the whole fan, final stage, and shroud as a unit. (P/N 17117561757)

Note: I should point out that since my car was not setting codes when the fan didn't work I can't guarantee the computer will continue sending a PWM signal after the initial 20 seconds.

Last edited by devlspawn; 07-02-2012 at 04:15 AM.
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Old 07-03-2012, 01:58 PM   #2
GSherbs
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thanks much for this!

I'll be doing my fan in short order as mine actually is setting a code (from bmw scanner 1.4.0):

# ERRORS DETAILS - DTC(hex)/PARAM(hex)
---------------------------------------------------------------------------------------------------------------------------
DME -> 7D/A1 - Electric fan, fault


I haven't done the troubleshooting you recommend yet but I will and I'll post my results once done.
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Old 07-08-2012, 09:50 AM   #3
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Thank you...

I have suspected my fan has been runnin incorrectly for some time now. Today I am replacing the final stage blower motor resistor for the interior HVAC, but I will be checkin the radiator fan like you explained. Question, my AC stops blowing cold air when I am at a stop light. I am assuming this is because my radiator fan is not working correcty. Should my ac keep running cool even when I am stopped completely? Thanks for the write up!
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Old 07-08-2012, 12:10 PM   #4
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ugh

Quote:
Originally Posted by devlspawn View Post
  • If readings on all those are ok then it's either the output final stage or the fan motor itself. You can check the motor by pulling out the fan and applying 12V directly to the motor (there is a small square plastic cap in the middle of the fan you can pop off for easy access).
In my case the motor would spin when powered so I figured it had to be the "output final stage". Unfortunately they don't sell just that part, you have to buy the whole fan, final stage, and shroud as a unit. (P/N 17117561757)

Note: I should point out that since my car was not setting codes when the fan didn't work I can't guarantee the computer will continue sending a PWM signal after the initial 20 seconds.

I do not know if it is sending any codes. My connections are displaying the correct voltages as far as I know. about .05v on the 3rd wire. It's either the motor or the connection.
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Old 07-09-2012, 08:56 AM   #5
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I haven't yet done any troubleshooting but I did experience something interesting this weekend...

I walk into the garage yesterday afternoon and find that my fan is spinning full bore. The car had been sitting in the garage for 12 plus hours and I know at least an hour prior to this that the fan was not spinning. Obviously, the car wasn't hot or even warm after having been in the garage since 11pm the evening prior...

I'm not sure what is wrong with my fan but, clearly, the motor itself is still good.

I disconnected the 3-wire fan connector and the fan obviously stopped. I did reconnect it about 10 seconds later and the fan remained off. However, since I am now paranoid that the fan running continuously at full bore like this will kill my battery, I am leaving it disconnected when the car is sitting in the garage.

Is this basically a fan-swap? Or is there a deeper electrical problem with my car?

I suppose I have to start somewhere and replacing the fan seems to be the right first step but if anyone has had similar issues, I'd love to hear about it.

Thanks!
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Old 07-09-2012, 04:58 PM   #6
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I'm also having issues with mine but my fan does not come on, Fuse# 37 keeps blowing and hot air comes out when the A/C is on.
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Old 07-10-2012, 08:13 AM   #7
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I'm also having issues with mine but my fan does not come on, Fuse# 37 keeps blowing and hot air comes out when the A/C is on.
Does the fuse blow right away? Sounds like a short somewhere - I'd suspect the fan motor/electronics are toast and blowing your fuse.

First thing I'd do is disconnect the fan, replace the fuse, and check for 12V across the main wires leading to the fan. If that is good and doesn't short out, the only thing left as the culprit would be the fan itself.
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Old 07-10-2012, 12:16 PM   #8
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Quote:
Originally Posted by GSherbs View Post
Does the fuse blow right away? Sounds like a short somewhere - I'd suspect the fan motor/electronics are toast and blowing your fuse.

First thing I'd do is disconnect the fan, replace the fuse, and check for 12V across the main wires leading to the fan. If that is good and doesn't short out, the only thing left as the culprit would be the fan itself.
Yeah, did that this morning. Fuse was fine until I plugged in the fan.
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Old 07-10-2012, 12:21 PM   #9
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Yeah, did that this morning. Fuse was fine until I plugged in the fan.
Sounds like a new fan is in order then.
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Old 07-10-2012, 03:59 PM   #10
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Is there anywhere you can get the final stage electric box without replacing the whole fan assembly
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Old 07-10-2012, 06:55 PM   #11
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Is there anywhere you can get the final stage electric box without replacing the whole fan assembly
not that i am aware of
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Old 07-13-2012, 07:01 AM   #12
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What temp should the aux fan kick in?

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Old 07-15-2012, 03:46 PM   #13
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Hey Fellas

Just an update...

Put the new fan in this morning and my problems appear to be solved.

The new fan behaves as it is supposed to according to troubleshooting - A/C on high, fan kicks on right away and my A/C is nice and cool. The old fan wouldn't come on even after waiting ten minutes.

I've cleared all my codes and we'll see how this goes over the long term.

If anyone is thinking DIY on this, it has to be one of the easiest jobs I've done on my car in a long long time. The only hangup for me was the plastic rivet on the drivers side of the fan... I couldn't get the centerpiece of the rivet to release at all... I ended up cutting off the top of the rivet with a hacksaw (after removing the second bit of the airbox intake) and wiggling the fan out. I then ended up carefully drilling out what was remaining of the rivet - doesn't take much as it is just plastic.

Fortunately i had the foresight to order a couple of rivets along with the fan I ordered so everything is fastened as it should be.
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Old 07-16-2012, 03:09 PM   #14
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Gsherbs... Good stuff!

I had mine throw a fan code so I am assuming that it went bad although I am not blowing any fuses. My fan never goes on at all. I am worried about over-heating in these high temperatures, as I did see the needle start to climb while I was stopped at a stoplight. I really wish I had an aux fan. Oh well. I am going to try to get a new fan and install it tonight to see if that fixes me up.
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Old 07-16-2012, 05:59 PM   #15
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i'd bet $1 that you'll be in good shape with a new fan!
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Old 07-16-2012, 07:14 PM   #16
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i'd bet $1 that you'll be in good shape with a new fan!
Well, $290 later... I'll have it installed by Wednesday and we'll see.
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Old 08-14-2012, 12:24 AM   #17
vinko2000
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Hi everyone, I have a problem with my fan also, after I turn the car off, the fan stay on for about 5 seconds, I think that is normal according what I read here, the bad thing is that the speed goes up considerably (when this happens I think that I am in a jet ready to take off), is that normal?, the Condenser and the Outside Ambient Temp Sensor where replace before this start happening...

If you need more information...
The a/c condenser was replaced after an accident on January 2011 when a was living in Seattle WA, it was a used one, I never use the a/c in Seattle, till I moved last December here to Nashville, and when the summer came I try to use the a/c, it didn't work, turns out the condenser had a big leak, at the moment I didn't have the money to replace it, so with a friend's help it was "repaired" with J-B WELD, but somehow the A/C wasn't working properly (I think the "Patch" obstructs the tubes* because I filled the a/c system with just one can of Freon), the air came just a little bit colder, I took the car to the body shop, they replace the Condenser and also the Outside Ambient Temp Sensor was missing, it was replaced. Now after I turn the car off the fan continue the spinning for about 5 seconds, but the problem is the speed, when the car and a/c are on, the fan runs with a normal speed, but after I turn the car off, the speed goes up considerably, making a very loud noise, people around look at my car wondering about the noise, when the a/c is off, the fan also is off, but when I turn the car off the fan goes on with the same ultra-fast speed and noise for the same 4-5 seconds... I took the car back to the body shop, but they said that the noise is normal; in the shop maybe the noise is not too loud because all the sound surrounded.
Any ideas what this is happening? do I need a new fan?, even when the air wasn't cold enough when the a/c was on, the fan was working fine before replace the condenser and temp sensor, I want to take the car back to the body shop, so they can check again, but I want to do it with some more information, so they can't tell me again that is normal. Thanks a lot guys.

PS. my car is an automatic 2000 323i...

Last edited by vinko2000; 08-14-2012 at 12:26 AM.
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Old 08-14-2012, 07:05 PM   #18
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Hi devlspawn,

Regarding your questions about measuring the output on the signal wire from the DME (to the fan controller): that wire is driven with an open collector of a transistor whose emitter is grounded (according to the Bentley manual). What that means is that the wire will be nominally 0V if you hook up a DVM to it. Basically, the DME does its signaling by changing the resistance of that wire to ground -- from maybe 100 Ohms or so to something much larger, maybe greater than 100,000 Ohms.

I measured that wire (with the connector to the fan controller detached) on my 1999 328i (manual transmission) with the engine running using an oscilloscope, and, indeed, other than some low level noise, the wire was at 0V.

To get a reasonable signal from an open collector output, you need to insert a pull-up resistor to the appropriate power supply lead -- in this case V+. So as to not risk damaging the DME, I put a 10,000 Ohm resistor (larger than it needed to be) between the signal lead and the +12V lead in the connector. Now, when the engine is off, that signal wire is a +12V. With the engine on, the wire stays at 12V for 9.5 ms and then goes down to ~0V for about 0.5 ms. Looked at as a positive signal, that is a 95% duty cycle square wave with a repetition rate of 100Hz.

After the air conditioner was turned on, that duty cycle slowly got smaller. One should start to see changes in less than a minute. I quit looking when the duty cycle continuously diminished to about 50%, because I was convinced that that meant the output of the DME was working as expected.

If you use a DMM with good filtering in the DC Volts mode, I expect you would read the highest voltage with the engine off, let's say, for example, 12.5V. Then, when the engine is running (and is not too hot) the voltage should drop 0.95 of that, or a steady 11.9V. After you turn on the air conditioner, it should slowly drop below that.

For my car, I haven't seen that the short fan turn-on at engine startup is a good indicator of the fan and controller working properly. In 5 or 6 startups, I only observed that once (with a recently purchased new fan assembly).

Also, unhooking the connector to the temperature sensor on the radiator outlet didn't cause the DME to activate the fan. I confirmed that both by measuring the signal from the DME with an oscilloscope and installing a new fan and looking to see if it started to rotate with this condition.

In my case, the problem was that the old fan wouldn't come on. After I took the fan assembly out I made some measurements on it. The signal lead measured about 1M Ohm or greater to both the V+ and ground leads. In the new fan, the resistance between the V+ lead and the signal lead was 1.48k Ohm. And between ground and the signal lead, > 1M Ohm.

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Old 08-14-2012, 08:30 PM   #19
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Im not sure if im having issues with my fan, but is it normal for the fan to be running almost all the time? I think i read somewhere that the fan runs at low speed when the temp goes above 94c but my runs at low speed before it even reaches that temp. Sorry OP I dont mean to threadjack.

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Old 08-15-2012, 01:12 AM   #20
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great work, thanks
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