Aux fan woes HELP!

[ninetyseven1]

mine is a 97 540i, my question is: Does the engine have to be at a certain temp before the DME will energize the low speed aux fan relay?? I have replaced fan resistors, check ALL fuses even big fuse 75, replaced low speed relay. I can jumper the relay socket pins 87 and 30 and the fan works on the lowest speed like it should, but it doesnt work with the relay in! I can jumper the temp switch connector near the radiator and the high speed works. Can someone please shed some light here?

[philly98540]

The temp switch on the radiator is a dual switch. It activates at two temps. The lower temp switch turns the aux fan on to low speed (normal speed). The higher temp switch turns the aux fan on high speed. You confirmed you can activate the high speed by jumpering the high speed switch. Can you make the fan run at low speed by jumpering the other terminals at that switch? The AC also turns on aux fan at low speed. Here is wiring diagram.


Speed1.png

[ninetyseven1]

The temp switch on the radiator is a dual switch. It activates at two temps. The lower temp switch turns the aux fan on to low speed (normal speed). The higher temp switch turns the aux fan on high speed. You confirmed you can activate the high speed by jumpering the high speed switch. Can you make the fan run at low speed by jumpering the other terminals at that switch? The AC also turns on aux fan at low speed. Here is wiring diagram.

Speed1.png

where is the low speed switch located?? i can NOT make the fan run on low by jumpering the low speed wire wire on that connector at the radiator, but I CAN make low speed come on by removing the brand new relay in the ebox and jumpering terminals 87 and 30 though.

[philly98540]

where is the low speed switch located??

Its part of the same switch screwed into the right side of the radiator. That one single part has two switches inside it.

i can NOT make the fan run on low by jumpering the low speed wire wire on that connector at the radiator, but I CAN make low speed come on by removing the brand new relay in the ebox and jumpering terminals 87 and 30 though.

If that is true and your actually jumpering the wires correctly at the switch, then you either have a bad new relay, or you wiring is broken somewhere. Check continuity between the connecter at the switch and at the low speed relay.

[ninetyseven1]

Its part of the same switch screwed into the right side of the radiator. That one single part has two switches inside it.


If that is true and your actually jumpering the wires correctly at the switch, then you either have a bad new relay, or you wiring is broken somewhere. Check continuity between the connecter at the switch and at the low speed relay.

this is the second brand new relay i have tried. Removing the relay each time and jumping the 87 and 30 terminals under it works to turn on the low speed just fine every time. So you are saying the wire from the dual switch at the radiator goes to the relay?

[philly98540]

this is the second brand new relay i have tried. Removing the relay each time and jumping the 87 and 30 terminals under it works to turn on the low speed just fine every time. So you are saying the wire from the dual switch at the radiator goes to the relay?

See wire diagram above. Switch goes directly to terminal 85 of the relay. The switch simply grounds out terminal 85 to activate the relay coil. Check that you have 12V at Terminal 86. This is what powers the relay coil and makes the fan turn on.

Jumpering 87 and 30 simply bypasses the relay altogether and does not test what you need to test right now.

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check fuse F20 is no voltage at terminal 86.

[ninetyseven1]

See wire diagram above. Switch goes directly to terminal 85 of the relay. The switch simply grounds out terminal 85 to activate the relay coil. Check that you have 12V at Terminal 86. This is what powers the relay coil and makes the fan turn on.

Jumpering 87 and 30 simply bypasses the relay altogether and does not test what you need to test right now.

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check fuse F20 is no voltage at terminal 86.

ok so if i have no voltage at terminal 86 then what? run a new wire from terminal 86 to where? OR is it safe to say of all else fails i can just connect a wire to terminal 85 and use an on/off switch to turn the fan on?

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and you said i can more easily test this all by testing fuse 20 in the glovebox and see if there is voltage?

[philly98540]

run a new wire from terminal 86 to where? OR is it safe to say of all else fails i can just connect a wire to terminal 85 and use an on/off switch to turn the fan on?

no and no.

and you said i can more easily test this all by testing fuse 20 in the glovebox and see if there is voltage?

If no voltage at term 86, simply check the fuse F20

[philly98540]

Ignore my hand written notes on the above pic. That was for soomething different.

[ninetyseven1]

Ignore my hand written notes on the above pic. That was for something different.

So what I see no voltage at terminal 86 and fuse 20 is good ?? Nobody knows?

[ninetyseven1]

alright so not getting any straight answers here, i am not an electrician i am a mechanic. Sorry, might have to ask a different forums or something.

[ninetyseven1]

time to start throwing parts at it i guess. New DME maybe.

[philly98540]

So what I see no voltage at terminal 86 and fuse 20 is good ?? Nobody knows?

I did not know you were totally inept at electrical. Sorry, my bad. You had the key on position 2 while checking for voltage at term 86? There is no voltage with key off. If no voltage at 86, check for voltage at both sides of the fuse. If you have voltage at both sides of the fuse, and none at 86, then your wire connecting from the fuse to the relay is likley bad.

[ninetyseven1]

I did not know you were totally inept at electrical. Sorry, my bad. You had the key on position 2 while checking for voltage at term 86? There is no voltage with key off. If no voltage at 86, check for voltage at both sides of the fuse. If you have voltage at both sides of the fuse, and none at 86, then your wire connecting from the fuse to the relay is likley bad.

so if this is the case, then can i just run a new wire from the fuse directly to the terminal 86?

[ninetyseven1]

so if this is the case, then can i just run a new wire from the fuse directly to the terminal 86?

Ok tested the 20 amp fuse F7 in the fuse box
And I get 12v with key on

[JimLev]

When are you going to test for voltage at 86??

[ninetyseven1]

will test tomorrow, didnt have time today or last night. So if i have no voltage at 86 on the relay terminal then i should connect a new wire from the fuse to the terminal 86 on the relay correct?

[philly98540]

I'd figure out why and fix it right and not run a jumper wire over to 86. I doublt the stock wire is bad unless some sketchy wiring work was done to the car in that area. In any event, if you think that you must hack a jumper to it, make sure you have a 5 amp fuse protecting it.

[JimLev]

Me thinks he's loading up the shotgun.

[ninetyseven1]

I'd figure out why and fix it right and not run a jumper wire over to 86. I doublt the stock wire is bad unless some sketchy wiring work was done to the car in that area. In any event, if you think that you must hack a jumper to it, make sure you have a 5 amp fuse protecting it.

i dont want to have to do that but like I said, I can jumper 87 and 30 at the relay's terminal and the fan works. Resistors are new, relay is brand new and ALL fuses good.

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So what if I do end up getting voltage at terminal 86 though? where should I be looking to next?

[JimLev]

One step at a time.

[ninetyseven1]

When are you going to test for voltage at 86??

Ok I have good voltage at 86, and good voltage at all
4 aux fan fuses , also
The medium speed at the temp sensor works now if I jump it , sooo ? Now what ?

[JimLev]

Referring back to post #2 schematic that Philly posted do the following (you may have already done some of this).

1) Pull the relay out of the socket, jump the socket connectors where relay pins 30 and 87 would be plugging into.
The fan should run at slow speed. Did it run, yes? Go to step 2.

2) With the relay back in the socket ground relay pin #85. The fan should run at low speed. Did it run, yes? Go to step 3.

3) Ground the black/red wire (SW/RT) at the temp switch on the side of the radiator. The fan should run at low speed.
Did it run? Yes or no? If no the wire between the relay socket at #85 to thee temp switch is bad.

Report back what you find.

[ninetyseven1]

One step at a time.

It was a bad ground at terminal 85

[ninetyseven1]

So ran a new wire from terminal 85 to ground and now low speed fan works , temps hitting mix of 102-103 while idling . Still too
Hot for this engine but I'm happy