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Auxiliary Electric Fan not working? Check the wiring.
The break was in the right side wheel well behind the splash guard.
If the fuse is good, then you may need to replace the wiring, not the fan - even if you measure 12VDC at the connector.

Apparently - corroded wires don't conduct current too well.
Can someone please reupload the pictures in this post? If not, can someone confirm that Apetrov1x5 is pointing to the correct wiring loom containing the aux fan power wires mentioned in SleeperE39's post?

Trying to figure out why my auxiliary fan won't turn on has been a nightmare and I'd like to confirm that this is the correct wiring loom before I start hacking it open. My symptoms are too similar to SleeperE39's.

Bought a new Depo fan off of Ebay and it doesn't turn on.

Tried to manually activate it using Inpa - nothing.

Checked the 50A fuse behind the glovebox - Ok.

Checked the connector on the car going to the fan and there is a constant 12V. Wtf is going on?
 

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Have you tried load testing your 12v supply? Rather than just using a meter if you hook up and old light bulb or something that takes a few amps to run. It is possible you are not getting a signal from the DME either because the wire is broken or the DME is not getting the info to know to turn the fan on.

Not sure if that is the correct harness but you would start at the plug and follow it back.

Check the small wire of the three for a pulsed signal both with AC on and off to look for a difference. Only the best meters pickup pulsed signals accurately but even cheap ones will show something even if it is just a different in different situations.
 

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Thank you Sailor24 - it appears that I bought a defective Depo fan from Ebay.

I load tested the 12v supply with an old light bulb like you suggested and it lit up fine.

As far as testing the small signal wire, I used a cheap voltmeter from Harbor Freight which didn't accurately pick up the pulsed signal, however I did see the voltage fluctuate between 1.3v - 1.7v while the car was idling in the garage for some time. The AC caused the voltage to drop by about 0.2v but it didn't always immediately spike back up after the AC has been turned off so I figured I'd do some more investigating.

In order to definitively confirm that I was getting a proper signal from the DME I used Inpa to manually activate the auxiliary fan and the voltage in the small wire dropped to 0.5v. Once the "test" was finished the voltage immediately spiked back up to around 1.5v.

This leads me to believe that the new fan is the culprit here. Lesson learned - don't cheap out when it comes to stuff like this.
 

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I can't speak for Depo but when mine failed I bought a batch of 10 for think it was 30 a piece or maybe that is what I sold them for? Cheap price but the quality was there. Kept 3 for my cars and sold the rest with no complaints. You just got a bad one so have them replace it and see how it goes. Warning though most after market and even a few OEM fans hit the shroud in front of the fan so test before the bumper. If it does touch just use a heat gun to soften the shroud and pull it out some.
 

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There is one more test you should do since it is easy. Back probe the plug with it connected to the fan and look for your 12v then activate the fan with INPA and confirm you still have 12v there. If you don't then it could be wires.
 

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Discussion Starter #46
My name was mentioned - thought I'd chime in.

My problem? I measured 12V at the fan connector
I put a scope on the PWM signal and it too was fine.

My problem was the wiring was FUBARED.
It was all burned from the connector all the way to the DME.
Insulation was hard, brittle, and touching it made it crumble.
With the insulation compromised the copper corroded.
I guess in the quest of light weight the German engineers decided 18awg (Sarcasm) was fine for a wire fused for 40A.

Not the first item in this car that had me thinking "What were they thinking?"
 
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