help diagnosing engine cooling fan

[Dr. Anthony]

Hey guys, My cooling fan is not turning on.

Here's what I've done.

- Tested my fan in a friend's 2011 m3 - It worked

I put it back in my car and started testing with a multimeter.
- Fuse has continuity. (fuse is OK)

I read online that the red wire on the fan has constant 12v? If thats true, mine does not.
Signal wire is getting signal. I believe I saw .05v at the signal wire. Again, since its just signal, it can't be a lot of voltage, and .05 is probably enough to signal it ON.

Ground is fine

there is no continuity between my red wire on the harness to the + terminal by the motor. Also no continuity between Red wire of harness (+) and the + side of the 40w fuse (I believe its fuse 88)



I also do this while ignition is on, or even when car is running. there are no changes.

The coolant temps are up half way so I know the fan should be running. I even have my AC blasted (AC should turn my cooling fan on as well)


I'm stuck, please help
Any assistance is greatly appreciated.

[THE TECH]

Kinda confused. Check where and when power is being applied in your friend's car and then see if yours has the same.

[Dr. Anthony]

He's unavailable until later.

I reworded my original post.
Do you know where the fan relay is?

[THE TECH]

Have you checked all your fuses?

[Dr. Anthony]

I've tested all the fuses behind the glove box

[M3PO]

Originally Posted by Dr. Anthony

He's unavailable until later.

I reworded my original post.
Do you know where the fan relay is?

This was my guess. Locate the relay, I bet that's the issue. Sounds like the only thing you haven't tested.

BTW, props to you for doing the diagnosing.

[s65e90]

relay, but if all is working it may/could be the coolant temp switch which would not allow the fan to come on but the fan would be fine.

[Dr. Anthony]

Originally Posted by M3PO

This was my guess. Locate the relay, I bet that's the issue. Sounds like the only thing you haven't tested.

BTW, props to you for doing the diagnosing.

I found a wiring schematic of the cooling system. I see the relay, I just have no idea where its located. I read somewhere that it may be under the pass seat. I checked and don't see anything.

Originally Posted by s65e90

relay, but if all is working it may/could be the coolant temp switch which would not allow the fan to come on but the fan would be fine.

The funny thing is, I have a brand new spare coolant temp switch laying in my tool chest. But I don't see why it wouldn't give 12v as the fan is supposed to get constant 12v, while the remote wire is what tells it to turn it on.

[Dr. Anthony]

**Just an update***

K, now I got 12v to the fan.
5.0 volts to the signal wire, but the fan still doesn't come on.
Fan tested OK on a friend's car tho.

[BPMSport]

Originally Posted by Dr. Anthony

**Just an update***

K, now I got 12v to the fan.
5.0 volts to the signal wire, but the fan still doesn't come on.
Fan tested OK on a friend's car tho.

You're going to have to scope the signal on that wire... it may not just be voltage.

[Dr. Anthony]

problem solved.

[M3PO]

Originally Posted by Dr. Anthony

problem solved.

Please explain.

[My Schnell]

Originally Posted by Dr. Anthony

problem solved.

Originally Posted by M3PO

Please explain.

Yes Please ...

[TMR]

Can i get the schematic to the cooling fan wiring?

[jeremyuhh]

reviving as im having the same issue. How was this solved @dr. anthony

[Shaneirle]

Originally Posted by Dr. Anthony

problem solved.

How did you solve this. Please I have exactly same problem and im not sure how to fix it

[CTMike]

Here was my experience while we look for Dr. Anthony to return.

—

Failed radiator fan replaced, picked it up a couple of days later… problem solved!

Not quite.

Drove it to my brother-in-law’s and had an OBDII reader hooked up to keep a closer eye on temps… no issues on the highway. I let it idle in the driveway just to make sure everything was good. Temps start climbing. Radiator fan never kicks in. I shut it off with first overheat warning at around 231 degrees.

Back to the shop (extremely apologetic and very determined to resolve the issue - they were great)… they replaced a fan relay under the passenger footwell, tested everything, and it didn’t overheat. I pick it up, let it idle in my driveway…. Temps start climbing, radiator fan never kicks in, I shut it off with first overheat warning at around 231 degrees. Sigh.

Back to the shop (even more apologetic and determined to resolve the issue)… They inspected the fan circuit again and found an overheated contact by the rear fuse carrier, near the battery. They think a high draw from the failing (old) fan was the cause. They restored said contact and things were running as expected.

—

No issues since!