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Thread: E36 318i Aux fan not coming on automatically

  1. #1
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    E36 318i Aux fan not coming on automatically

    Hi there, my aux fan is not working.

    The car (1998 318i) kept overheating, and stupidly I never realised that the aux fan wasn't working. When I checked the fan, it had seized. I loosened it up, and connected it directly to battery, but it wouldn't work. Replaced the fan, which does work directly connected, but doesn't come on as it should when it is part of the system.

    Any ideas what the seized fan trying to come on but not able to has taken out - fuses/relays? The fuse looks ok, and have replaced it with same, but still nothing. Wondering if it's the relays, but am not sure how to confirm this? Have tried closing the contacts on the temperature sensor side of the radiator, and I can hear a clicking - which i'm assuming is the relays. Is the clicking a good or bad sign?

    Got a cheap OBD, but then found out the car doesn't have connector in the cockpit, so have ordered 16-20 pin adaptor (still waiting) for the port in the engine bay. I'm hoping that would confirm if it was the relays, but I don't know if this is hoping for too much?

    This may be a really simple thing, but it's giving me a bit of a headache. More than happy to replace relays - if I know it is them, but don't want to clutch at straws.

    Any suggestions of any tests I can do to pinpoint where the system is falling down?

    I just need the fan to come on in normal operation, and help from anyone who knows a lot more than I do about this would be greatly appreciated. Cheers - John

  2. #2
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    Is there a plug with 3 pins on the passenger side end of the radiator? That is the temp switch to control the fan. If you unplug the connector from the sensor/switch and (with the key in run pos) use a little wire or paperclip to short the brown wire to one of the others, one should cause normal speed to run and one should cause it to run high speed. That will confirm the relays and all wiring is ok. Try that and report back.
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  3. #3
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    Quote Originally Posted by toojohnny View Post
    ...Have tried closing the contacts on the temperature sensor side of the radiator, and I can hear a clicking - which i'm assuming is the relays. Is the clicking a good or bad sign? ...
    Quote Originally Posted by jc43089 View Post
    Is there a plug with 3 pins on the passenger side end of the radiator? That is the temp switch to control the fan. If you unplug the connector from the sensor/switch and (with the key in run pos) use a little wire or paperclip to short the brown wire to one of the others, one should cause normal speed to run and one should cause it to run high speed. That will confirm the relays and all wiring is ok. Try that and report back.
    I think he's tried that.

    John - clicking is good in that it means the relay is getting power but it doesn't mean the relay is working. If you bridge the temp switch pins and the new fan doesn't come on then it's likely to be a relay whether you can hear it click or not. What happens when you bridge the centre pin of the temp switch connector with the other pin? Try swapping the two fan relays and see if you get a different result.

    If you've still got the bumper off and you've got no joy then bridge the pins and check if you're getting 12v at the fan.
    '96 M3, S50B32, 6MT
    + good stuff

  4. #4
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    Hi there,

    Yes, as you realised, I have tried bridging the connectors for the temp switch (brown to both low/high speed), and the fan does not come on (just very apparent clicking on the relays). When you say swapping the fan relays, do you mean with new ones, or with each other? They are different colours, and I assume these are not interchangeable?

    As mentioned in my original post, the fan does come on when connected directly to the battery, but that's the only way.

    The bumper isn't off the car.

    Does it look like the relays? Would they have been fried if the previous fan was seized? I wanted to try and be sure, before I buy 2 new relays, and then t still might not work.

  5. #5
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    The low-speed fan relay is yellow and is identical to the A/C compressor clutch relay left to it. So you can use the A/C relay and plug it in the low (normal) speed fan relay socket.
    The high speed fan is another type, not interchangable with the A/C or low-speed fan relay.

    First do the A/C relay <---> low speed relay swap and see what happens if you trigger the low speed fan by bridging the connectors for the temp switch..

    It would be very odd that both relays would have died.. I'd expect the fuse to die if the fan gets stuck, not directly the relay.. And especially not both of them.
    If both relays are nicely clicking then it would be very odd if both of them are dead, but theoretically it's still possible..

    So let us know what the A/C <--> low speed relay swap does..

    Then, if that doesn't solve it (at least the low speed fan), then I'd suspect the wiring. If the relay successfully puts +12V on the wire to the fan, but it somehow doesn't arrive there then it should be the wire.

    If you manually test the fan, do you also feed it another ground than the factory wiring is providing normally?

    Perhaps, the ground wire is dead, or the wire isn't connected properly anymore to a ground point of the chassis?
    That would be a logical explanation: temp switch working, relays happily working and clicking, +12V supplied to the fan, but no ground available, so "no go", no matter if it's low or high speed..

    The chart on this page says ground comes from X1890, ground distribution 0670.4 and the finally X165, which is the same ground as the dual temperature switch in the radiator uses. Chart here: https://www.bimmerforums.com/forum/s...speed-troubles .

    Also (or perhaps best as first step), while supplying ground to the low- or high speed wire at the temp switch connector in the radiator, double check with a multimeter if the aux fan connector (which should supply 12V and ground to the aux fan) receives +12V (pin 2: normal speed, pin 3: high speed) and proper ground (pin 1). I've written this in a couple other threads already: if you don't have a multimeter, go and buy one (shouldn't cost more than $10-$20 for a standard one) and watch some multimeter tutorials on youtube.. Will be one of the best investments you can make, and will improve your DIY skills a lot, both with cars and also in the house.
    Last edited by ed323i; 07-06-2018 at 07:40 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  6. #6
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    Yep, that ^
    '96 M3, S50B32, 6MT
    + good stuff

  7. #7
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    Hi Ed, I swapped the relays, and it made no difference. You might have to bear with me a little here, as I'm trying to learn and understand as I go along.

    So, if the fan 'works' directly when connected to the battery, then you are saying the connector might not be supplying power? I do already have a simple multimeter (analogue) although I'm still trying to learn how to use that too. I did have a look on the internet, but I need something specific to what I am doing. Pin 1 (presumably the top one of the 3) would be connected to the negative or positive probe? I'm also not entirely sure what setting to pick on the multimeter. This will need to be in quite simple terms, as I'm good at picking things up, but my current knowledge is pretty low! I am trying to find some multimeter info/tutorials right now!

    What do you mean by supplying ground to the low or high speed wire on the temp switch connector? Thanks

  8. #8
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    I have tried to use my multimeter (best I know how) on the connector, and I'm getting nothing. I connected the black lead to Pin 1 socket, and then tried red to both 2 and 3. I didn't do anything else (ie supplying ground to the low or high speed wire - because I didn't know what to do) so am I doing something wrong, or not doing something I should be in addition?

  9. #9
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    OK.. Great job.
    I'll try to guide you through..

    With ignition on, and the temperature switch connector bridged to either low or high speed (low or high speed relay should click), you can check if +12V arrives at the aux fan connector by:
    * setting the multimeter to 20V DC (DC is often depicted as a horizontal line with three short horizontal lines below)
    * connecting the black lead to a good ground. I mostly use one of the three bolts on top of the shock tower
    * connecting the red lead to pin 2, and next to pin 3. One of them should show +12V depending on which combination of pins you bridged at the temp switch connector.

    What you'll probably find, is that indeed it shows +12V (pin 2: normal speed, pin 3: high speed).

    What I suspect is that there is no ground on pin 1. You can test this by:
    * turning off ignition (not needed for this test)
    * setting the multimeter to 100 Ohm setting
    * connecting the black lead to a good ground. I mostly use one of the three bolts on top of the shock tower
    * connecting the red lead to pin 1 of the aux fan connector. If the pin 1 has ground, it will show somewhere between 0 and 1 Ohm. If it has no ground, it will show infinite (very high) ohms.

    Once you've done these two tests we'll know the cause and we'll be able to solve it (probably checking the ground; disconnecting a ground wire, cleaning the connector and ground point reconnecting it).
    Last edited by ed323i; 07-07-2018 at 01:05 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  10. #10
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    Hi Ed, great description. Very easy to follow :o)

    With the 12V test, I'm still getting nothing. With the ground test, I did indeed get 0 - 1 ohms as you said.

    So ground appears ok after all, and it is the wiring? If that is the case, what might be stopping it? Is it possible the wire/cable can physically fracture, or could there be something else blocking the voltage coming through?

    With regards to the old seized fan, is it likely that the seized fan has created an electrical problem, or an electrical problem not supplying power to the fan, and it seizing through lack of use? The first option would seem more likely wouldn't it?

  11. #11
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    I think the low speed and high speed fan relay socket is connected directly to the two +12V wires going to the fan.. So, if the relay clicks and supplies the needed voltage, then the problem must be in the wiring.. You'd have to open up the fuse box and perhaps you can see some damage there.. Or, you can install custom wires.. But, because it's quite high power (20-30 Amps) it has to be done with a high quality bond and good shielding, otherwise you're asking for engine bay fires.

    Okay.. One last test..
    Remove the low-speed and high speed relay. Using the multimeter in the 20V DC setting, black lead to the shock tower bolt, and red lead to one of the pins of the relay socket, see if you can find +12V on one pin with ignition off, and on two pins with ignition on. So, both the low-speed and high-speed relay should have two pins with +12V with ignition on.

    If that's okay, then one very last thing you can do, is bridge the power directly from the relay socket. But, if you bridge the wrong pins, you CAN cause damage here.. So, it's important to bridge the right pins, double checking the relay pin numbers. If even then the fan doesn't turn on, then it must be the wiring. It probably melted at some place, which would be odd, because the fuse should have protected the wires.

    P.S. Here's a chart: https://www.bimmerforums.com/forum/a...8&d=1525127055 (ignore the mods)
    You'd have to bridge between pins 30 and 87. Be sure to 'mirror' correctly looking at the bottom of the relay and projecting it to the relay socket.
    Last edited by ed323i; 07-08-2018 at 07:52 AM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  12. #12
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    Hi, I removed both relays and tested the sockets for voltage. I was getting nothing at all with ignition off, but with ignition on I'm getting voltage from 1 pin on each relay socket: Top pin 86 on high-speed purple, and right pin 85 on low-speed yellow. Bearing in mind you said I should be getting voltage from 1 socket ignition off, and 2 ignition off, I am getting a -1 both times. Does this clarify much?

  13. #13
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    Yes, it clarifies things..

    Looking at the chart https://www.bimmerforums.com/forum/a...8&d=1525127055 :
    There should be a constant +12V high amps (big wire) connected to pin 30 on both relays. That should a hard-wired +12V coming from the +12V battery terminal in the engine bay (318i has battery in engine bay). Pin 85 should receive +12V once the ignition is on.

    Could it be that with the high speed relay it's coming from pin 30, as the relay socket is rotated 90 degrees compared to the two relay sockets besides it (A/C clutch and low speed fan relay)..

    Ah, one correction: With both relays out, ignition off, there should be +12V on pin 30 of the high speed relay socket. And, because the high speed relay feeds the power to the low speed relay, only when the high speed relay is off (so, the high speed relay shuts off the low speed relay when the high speed turns on), there won't be +12V on pin 30 of the low speed relay.

    So, can you verify this:
    With ignition on, there should be +12V on pin 30 AND pin 85 of the high speed relay.
    With ignition on, and the high speed relay not plugged in, there should be +12V on pin 85 of the low speed relay.
    With ignition on, and the high speed relay plugged in, there should be +12V on pin 85 AND pin 30 of the low speed relay.
    Also, check if fuses 41 and 16, in the fuse box, are okay. You can verify this by taking out the fuse, using the multimeter in 100 Ohm setting and connecting black lead to one end/pin of fuse and red lead to the other end of the fuse. Should give 0 to 1 Ohm if it's okay.

    Again double check the pin numbers, by orientating the relay above the socket, then looking below the relay for the pin numbers, and projecting those numbers on the socket. Check for correct orientation. The linked chart above is orientated correctly, I believe.

    Can you recheck, and let me know the results.. Then we should be able to find the solution..
    Last edited by ed323i; 07-08-2018 at 11:26 AM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  14. #14
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    Hi again, I have done the tests you said (some of which I had already done on my previous message) but more in this instance is good!

    Ignition on for all tests:
    1. 12V - to 86 only on high speed relay.
    2. H/S out - to 85 only on low speed.
    3. H/S in - still to 85 only on low speed.

    Looking at the diagram, the orientation is good for the low speed relay, but not for the high speed (and naturally you'd expect the orientation to be consistent within the same diagram). The high speed does only fit in the socket one way. 12V is going to the top - which is perpendicular 86, rather than horizontal 30. Mine is 86 at the top and 87 at the bottom. It's at 90 degrees anti-clockwise to the diagram.

    So this clearly looks like I'm getting nothing at socket 30 for either relay.

    16 fuse is good. Mine doesn't have a 41 fuse.

  15. #15
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    OK.. I think we have found the cause now..
    Fuse 41 is missing.. I think it's a 30 Amp fuse, but you can double check on the inside of the lid of the fuse box.

    Without that fuse, socket 30 won't get it's +12V high amps supply, and that would explain it all.

    P.S. Perhaps my high speed relay socket is not in its official orientation due to a previous owner/mechanic taking it out and reinserting it with a wrong orientation. I actually adjusted the chart, but perhaps not based on the stock orientation.
    But +12V on pin 86 can't be correct. That would cause a short, because pin 86 should receive a ground signal from the temperature switch, once the high temperature is reached.. Or there must be a difference between European and US relay wiring, which would be odd.

    P.P.S. Added fuse locations:
    E36 325i Fuse & relay diagram.jpg

    Check on the bottom left: "auxiliary fan: 16,41"

    And you're right.. My high speed fan relay socket is rotated 90 degrees.. Stock, it should be orientated identical to the A/C and low speed relay (and all other relays). Random E36 fuse box photo from Google:
    photo0167-800x600--10481c8.jpg
    Last edited by ed323i; 07-08-2018 at 05:01 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  16. #16
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    Oh boy.. And you're also right about pin 86 receiving +12V and pin 85 being connected to the high speed/temp part of the temperature switch:
    Attachment 633404

    Now to double check if it's different wiring with the M52 engines (which mine has).. Very odd..
    I see what has gone wrong.. I used the chart on this page, https://enderw88.wordpress.com/2012/...ioning-relays/ . And it has the 85/86 connections wrong way around it seems.
    But the odd thing is my mod (in the signature, to immediately trigger high speed fan instead of first triggering low speed fan) did work just fine, bridging between pin 86 of the low- and high-speed relay sockets.. Very odd.. But getting off topic here.

    To complicate matters even more, some E36s use fuse 48, in the auxiliary fuse box (I don't know where that is).. See chart above..
    Found description and layout of the auxiliary fuse box here (scroll down a bit): http://knigaproavto.ru/shemy/en/bmw/...x-diagram.html .
    Quite complicated. But, as you seem to have both low- and high speed aux fan relays in the normal fuse/relay box, I think fuse 41 in the normal relay box should be the culprit..
    Last edited by ed323i; 07-08-2018 at 05:11 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  17. #17
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    I was a bit excited there, thinking we (well you) had narrowed it down to a missing fuse (apart from the fact I know I've never removed any fuses).

    It simply isn't supposed to have one there. It says 16, 48 for Aux fan 4-Cyl (16, 41 seems to be for 6-Cyl or diesel) But my fuses only to up to 46, so i'm wondering is there another fuse which is causing an issue, or is it not the fuses at all?

  18. #18
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    Is the fact I can't get any voltage on the 30 pins the whole issue here? And it's now 'just' figuring out why? Hopefully we can assume the wiring (ie power lead to fan) is ok for the moment?

  19. #19
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    Yes, correct. Wiring should be okay.. No voltage on pins 30 is the cause..
    Probably is the fuse, which in your case is in the cabin, driver side.
    See http://knigaproavto.ru/shemy/en/bmw/...x-diagram.html and scroll down a little (search for 48)..

    And, it's the probable cause, as the fan got stuck and the motor in the fan can then suck more amps than normal, causing the fuse to burn..


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  20. #20
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    Hi Ed....finally working! It was indeed the 40amp fuse in the cabin. I got your message at 2am UK time, but I still went outside and had a look - as I was so eager to confirm it. 90 minutes later of removing panels/checking/looking on the net to reconfirm/rechecking....the fuse on my vehicle isn't on the drivers side low, or the passenger side low - Mine was higher up behind the glovebox (seems to vary so much between models etc). Even then the guy in the car parts store was insisting I would want smaller fuses. Good thing I didn't listen to him, as once I'd got the fuse in (and I wanted to do it tonight!), I manually closed the contacts on the temp switch, and it came on :o). Then filled up the system/bled to eventually see it coming on in normal operation depending on temperature.

    Thank you so much for your patient and very detailed advice. Would have been pretty stuck without you! A real credit to these forums. Indebted to you!

  21. #21
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    Sounds like you were in a pickle, this was a real head scratcher. It's lucky Ed has the patience of a saint in order to help a lame dog over a stile and that you stuck to your guns and bought the right fuse. I thought it was a lost cause but I guess I'm laughing on the other side of my face now. It was a rollercoaster ride but all's well that ends well and now everything is coming up roses.

  22. #22
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    Well unlike some people (who can be arrogant on forums), he was the opposite. Not sure about the lame dog bit? He was very patient - and willing to explain in detail his thoughts, and ideas. Fortunately I have enough nous to be able to follow exactly what he was saying, and be confident I had done it correctly (the relay sockets for example). Great guy, and I've learned some really useful electrical tips and processes to boot. Very satisfying to be able to be guided through something like this, as opposed to being ripped off by a garage, and can't thank him enough. Luckily I had someone as good as him reply.

  23. #23
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    Thanks for all the credits. And really glad we managed to fix it!

    I also really like the fact that you learned a lot from the experience. I myself learned some things too in the process. I'm a bit of an intuitive guy and felt it was worth the effort to help you out, and I also sensed you were a quick learner. It was great and rewarding to guide you through :-) . Also, I'm thankful for the guys who gave me feedback on the questions (like the fan delete mod, and the special electric mod I had in mind w.r.t. the high-speed/low-speed aux fan relays, which eventually didn't turn out it be a worthwhile upgrade) I had in the recent past. So I'm sort of passing it on... It's a great forum!
    Last edited by ed323i; 07-10-2018 at 05:33 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

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