Fan FCM questions

[daught]

Both my fans stopped working all of a sudden. The highway was crawling very slowly and my temp went up. I polled over and neither of the fans was on. I tried with A/C on LO and the AC fan did not come on. AC was fine a few days ago.

Does the FCM control both fans?

If one fan is shorted would both fans stop working?

From what I read the FCM has two power wires going in to it and two control wires.

power
brown - ground
Red/Blue- constant 12v from fuse S42

control
red/white- acc 12v from fuse S4
red/gray - Signal

How does the ecu control the two fans independently with one signal wire??? Can someone direct me to the wiring schematics?

[diagnosticator]

The FCM has two sections, one for the left radiator fan, and the other for the AC condenser fan. They are independent from each other. The radiator cooling fan is controlled by the engine ECU. The AC condenser cooling fan is controlled by the HVAC controller in the dash panel. Both controllers send a PWM voltage to the FCM to start the fans and control fan speed. There are not two power supply wires to the radiator fan.

[daught]

And what's the preferred replacement other than genuine $$$

[diagnosticator]

And what's the preferred replacement other than genuine $$$

A good used OEM genuine FCM. Check the fuses.

[daught]

The FCM has two sections, one for the left radiator fan, and the other for the AC condenser fan. They are independent from each other. The radiator cooling fan is controlled by the engine ECU. The AC condenser cooling fan is controlled by the HVAC controller in the dash panel. Both controllers send a PWM voltage to the FCM to start the fans and control fan speed.

So then the info is wrong and both thin wires are for PWM signal?

If the two sections are independent I must not have power to the FCM then, right? How else would neither fan work.

[diagnosticator]

So then the info is wrong and both thin wires are for PWM signal?

If the two sections are independent I must not have power to the FCM then, right? How else would neither fan work.

No way to control separate fans with one Fan speed PWM signal wire. Check the fuses.

[Preston_08]

Both my fans stopped working all of a sudden. The highway was crawling very slowly and my temp went up. I polled over and neither of the fans was on. I tried with A/C on LO and the AC fan did not come on. AC was fine a few days ago.

Does the FCM control both fans?

If one fan is shorted would both fans stop working?

From what I read the FCM has two power wires going in to it and two control wires.

power
brown - ground
Red/Blue- constant 12v from fuse S42

control
red/white- acc 12v from fuse S4
red/gray - Signal

How does the ecu control the two fans independently with one signal wire??? Can someone direct me to the wiring schematics?

Both my fans burnt up not long ago. Didn't know it was the fans til I replaced everything I could besides those and didn't think to check them individually. Replaced my relay and the FCM before changing my fans. Tested my fans after I got new ones and they was both fried, wouldn't move an inch. I just never woulda thought both fans would die at the same exact time. Working like a champ now


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[daught]

Anyone have the wiring schematics? It would make troubleshooting way easier.

Good thing I am starting my timing belt today. It will be nice and open for testing fans.

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[Preston_08]

Anyone have the wiring schematics? It would make troubleshooting way easier.

Good thing I am starting my timing belt today. It will be nice and open for testing fans.

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Might be able to google some...just used my Bentley manual for those. You check the huge blue fuse under the dash on the drivers side? Sometimes that blows out.


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[daught]

I get power and ground on the big wires. One of the small wires is 12v and the other is PWM. So up to the FCM plug it's all good.

When I turn on the car the PWM is around 0.3v, AC on 1.8 , car hot no AC 1.9v, car hot and AC 2.5v.

Whole fan carrier is coming out tomorrow, I will test the FCM outputs and fans themselves.

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[Preston_08]

I get power and ground on the big wires. One of the small wires is 12v and the other is PWM. So up to the FCM plug it's all good.

When I turn on the car the PWM is around 0.3v, AC on 1.8 , car hot no AC 1.9v, car hot and AC 2.5v.

Whole fan carrier is coming out tomorrow, I will test the FCM outputs and fans themselves.

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If your fans are toast I recommend these aftermarket fan https://www.europaparts.com/dual-rad...8e0998455.html

They had great reviews and are built better than the originals in my opinion, moves a ton of air.


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[daught]

Will keep those is mind. The FCM power pin broke off from corrosion.



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[<3Quattro]

Isn't there a way to test the fans by jumping wires directly to a 12v supply to rule out the fan motors being bad

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[Preston_08]

Will keep those is mind. The FCM power pin broke off from corrosion.



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Time for a new FCM that's sucks though

And yes, just splice into the wires of the fans from a jump wire from the battery.

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[monky]

I have a similar issue if anyone can assist with this overheating issue. 2004 Audi A4 1.8T Quattro Avant. 165k miles.

I was on the highway in stop & go traffic one day & the temp gauge started going up slowly. Then the coolant warning came up. I pulled off the nearest exit & was able to park at an Advance Auto. Popped the hood & there was coolant in the reservoir tank between min & max. I noticed that the fans did not spin. I let the car cool down a bit & drove home, the temp gauge went back down to the half way point & stayed there. I started googling the symptoms & apparently the FCM is known to go bad on these cars. I checked the fuse on the left side of the dash & the 5A fuse was ok. So I ordered a replacement FCM by Doorman from rockauto & my friend installed it for me. Fans still do not spin & the temp gauge will go up if I'm not moving but will start to go back down when I get going.

Can it be the fans? Is there a relay that may have went bad? Where is the relay & how can I access it?

I'm frustrated & about to go to the stealership. Any help or advice is appreciated.

[5ktq]

Does the little fan spin up when you turn the AC on? it should, no matter if the car is hot/cold.

There's one relay in the ECU box, under the ECU. possibly another by your knees, inside the car.

Fuses im not sure, i think also one of those locations.

[monky]

The fan does not spin with the AC on (temp set to LO & speed all the way up).

[Preston_08]

Should've checked your fans before ordering a FCM. There's a relay in the ECU box, and there is a big blue fuse under the knee bolster below the steering wheel. New Relay is $40 and idk about the big fuse. Scroll up and you can find the fans I put in my car since both of mine was burnt up. Test the fans directly by using your battery and jumper wire.


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