Engine Fan not working! Please HELP

[MarekJ]

Hello. I have a 2003 A4 B6 1.8T Quattro Automatic Sedan.

My engine fan is not working. I tried everything and searched the forum for answers.

I replaced the Engine Coolant Pump
Radiator Fans
Fan Control Unit and Circuit Breakers
A/C Compressor
Flushed the cooling system.
I Check ALL the circuit breakers drivers side and near the ECU.

I hardwired the fans to the battery and they DO work. but through the Fan control Unit, they DONT
NONE of the two fans work.

I have still yet to replace the coolant temp sensors.

any ideas?

Thank You

[imnuts]

What is the engine temp when you're testing them? Does the one turn on if you turn the AC on? Is the FCM getting power?

Sent from my Pixel 2 XL

[old guy]

The temperature sensor in the lower radiator return hose is the one that sends a signal to the fan control unit. Are you getting any dtc's related to the cooling system?

[MarekJ]

What is the engine temp when you're testing them? Does the one turn on if you turn the AC on? Is the FCM getting power?

Sent from my Pixel 2 XL

Engine is warmed up to operating temp, A/C is on Max AC with blower fan all the way up and them on LO. None of the fans turns on.

[MarekJ]

What is the engine temp when you're testing them? Does the one turn on if you turn the AC on? Is the FCM getting power?

Sent from my Pixel 2 XL

The FCM is getting power only from one of the 4 ports on the plug, i tried testing it with a tester. Not sure about the other 3 ports. None of the fans turn on with the AC on. Not sure how else to test FCM i dont have the software VAG COM.

[MarekJ]

The temperature sensor in the lower radiator return hose is the one that sends a signal to the fan control unit. Are you getting any dtc's related to the cooling system?

The only message on the dashboard I get is when the engine overheats in traffic I get coolant message. It makes sense about the lower coolant sensor might be bad, but why is the other FAN not working for the AC? one is for the engine other is for the AC and neither of them are working. Thank you.

[MarekJ]

Bump.

[imnuts]

Have you tried searching for other threads on the FCM? There are several of them, and just browsing the results quick in my phone, there are many with very similar symptoms that you have posted.

Sent from my Pixel 2 XL

[krazeedrivr]

2005 Audi A4 B6 FWD(cvt) 1.8t

I'm in the exact same situation as you, neither the rad nor the AC condenser fan work at all. Eventually the car overheats in stop/go traffic.

I replaced the fans with new and tested working ones, new radiator and coolant, 3 different FCMs from different manufacturers, new lower coolant temp sensor, I checked the ECU enclosure and it is dry as a bone with no rust on the wiring or relays (Tx heat - little rain) even so I replaced fan relay 219 to eliminate that possibility, then I checked every fuse in the fuse box and in the ECU enclosure under the hood visually and with a fuse tester on 3 separate occasions. I hadn't replaced the second CTS, but to my knowledge it doesn't control the fans, and my coolant readings always seem accurate in Torque and on the dash. Also recently replaced the condenser coil and compressor about a year ago.

VCDS had shown DTC 18080 for the "fan control module open to ground" a couple times while doing replacements and tests, but I hadn't seen it come up in a scan recently after clearing DTCs. Also tested the cable coming from the ecu going into the FCM. I get 13.7+ volts on one of the 4 paddle/pins.

One time during a FCM replacement while the car was off, when I finished the last wire connection for the AC condenser fan, it kicked on by itself. I thought I had some progress so I went and started the car, but soon after the fan shut off even with AC on LO with recirc on. It never came on again since, so this seemed like an electrical anomaly related to my replacement and testing, maybe like the fan relay stuck open until I started the car or something.

I have scanned this forum and many others for this issue and there isn't anything I haven't done replacement part or test wise, that I have found documented at least. I do not have a registered version of VCDS-Lite so I hadn't been able to do output tests though. I do not know exactly how the circuit works beginning to end so my guess might be way off base, but it seems that the ECU is not commanding the relay to function correctly, thereby getting juice to everything down the line.

I am about to take it to an auto electric specialist here in Dallas Tx, but I hate giving up. I'm not a whiz with an Ohm meter, but I'd be glad to try any electrical tests if someone can describe the procedure(s). Wiring diagrams would be helpful as well if available.

[Wheelbarrow]

I just solved my fan problem this past weekend. Here's what I initially replaced/checked:

*219 relay
*replaced fans completely
*Coolant Temp Sensor
*replaced FCM twice (once with a cheap one and once with a not so cheap one)

But the real culprit was a large fuse located under the dash. You have to remove the lower cover to get to it. For the 3.0 liter it's a 60 amp fuse. It may be a different amperage for the 1.8. Anyway, mine was completely roasted. I replaced it and the fans now work perfectly. I suspect that my old fans were causing a larger draw on power because they were worn out causing things to fry. So, although replacing the fans didn't solve my problem initially, it's probably good that I did, as I most likely would have blown something else out after a while.

Here's the location of the post that helped me find the problematic fuse: https://www.audiworld.com/forums/aud...-fans-2786886/ Keep in mind in this post they are talking about AllRoads, but it apparently applies to our vehicles as well. Good luck! I feel your pain. I was certainly baffled (and a bit enfuriated) by it all.

[Gin+]

You can check for voltage and PWM signal (signal that tells the fan controller to turn fans on) using a multimeter on input leads of the fan controller. Best way to trigger the fans is by using vcds to run a fan output test. The PWM signal generates a really low signal voltage but nonetheless, readable enough on a DMM.

[krazeedrivr]

Checked under the dash behind the knee panel and found that 60a fuse and some relays along with a couple other fuses. Visually inspected, they all looked fine. I hooked my multi-meter up to the FCM cable from the ECU and I did find .5 volts on one of the other pins. Doesn't seem to change though regardless if AC is on LO, car is overheating, or even if the car is off.

I don't have a registered version of VCDS, and just using a cheap vag com clone cable instead of a Ross Tech, so I can't do output tests. If there is a way to do it I am not understanding with that setup let me know. I agree, it would be nice to verify the ECU can command the fans on and therefore the entire circuit, but after replacing or verifying everything but the ECU it seems that would really only be testing the one part I hadn't replaced, the ECU. Still open to more testing or suggestions though, even if I've done it before.

[Gin+]

Can't recall the wire colors off the top of my head but alas, this was posted on the vcds forum;

Pin 1 = Ground, usually a large brown wire
Pin 2 = 'Switched On' power, small wire
Pin 3 = 'Fan Control' from ECM - PWM signal
Pin 4 = Power, constant - large red and ???

The last time I went thru this without full VCDS I cleared codes, started the car and had a buddy cycle econ on and off while checking the PWM signal wire with a DMM. I don't remember what the readings where as I mainly was just looking for a slight change in values, but half a volt sounds plausible. Of course I did this after the FCM power leads tested okay. In my case, the fans ended up being faulty.

[krazeedrivr]

Can't recall the wire colors off the top of my head but alas, this was posted on the vcds forum;

Pin 1 = Ground, usually a large brown wire
Pin 2 = 'Switched On' power, small wire
Pin 3 = 'Fan Control' from ECM - PWM signal
Pin 4 = Power, constant - large red and ???

The last time I went thru this without full VCDS I cleared codes, started the car and had a buddy cycle econ on and off while checking the PWM signal wire with a DMM. I don't remember what the readings where as I mainly was just looking for a slight change in values, but half a volt sounds plausible. Of course I did this after the FCM power leads tested okay. In my case, the fans ended up being faulty.

Gin+ thank you for that information. It took me a while to test this again, but I am getting some different results and its very curious.

Confirmed colors:
Pin 1 = Ground, large brown wire
Pin 2 = 'Switched On' power, small red/white wire
Pin 3 = 'Fan Control' from ECM - PWM signal , small red/silver grey wire
Pin 4 = Power, constant - large red/blue wire

Test results:

So on pin 2, I am getting 12.5 volts when the car is off, even if the key is out of ignition, or 13.7 if the car is running. It has no other values regardless of AC on or not.

On pin 3 I am getting .3 volts if the car is off, even if key is out of the ignition. If the AC is on its .3 volts until I turn the AC to LO and then it goes up to between 2.5 - 3 volts. I am guessing we are seeing alternating PWM signal for the fan.

Now for pin 4, I get nothing on it. Car on or off including key out, AC on/off or LO. I'd swear I used to get juice on it, but now nothing. I didn't let the motor run very long during testing, maybe a couple minutes 3-4 separate times. Definitely not long enough for it to warm up. Should it be constant juice? Do we know what controls this pin 4? Is this line switched by the relay, or fused?

[krazeedrivr]

OK I fixed it, and I feel like an idiot. It was that 60 amp fuse that Wheelbarrow had previously mentioned. Making me do that test with the meter and questioning why the constant power line was off was key to make me get technical enough to fully understand the circuit. I confirmed using this wiring diagram where pin 4 came from(S42 40a in the pic), and traced it to the fuse. I kept looking at that fuse thinking it would look burned out, and said well since I have it out I should at least test it, and lo and behold that was it. Bottom line is I'll never trust a visual confirmation on a fuse again.

As a means of a small writeup post investigation and fix to give back to the community, this is how I would confirm this circuit again (in order) in the future if it recurred. Thanks to WB and GIN for the help and direction!

1. Pull the fan fuse under the dash and test it with an actual fuse tester (don't just verify visually)

2. If that fuse is good, then do the voltmeter test. If you get the results I got on pins 2 and 3, but also juice on pin 4 then it would appear that is all good from the ecu, fuse, and the FCM input. Using your voltmeter, put the black probe into pin 1 and test pins 2-4 with the red probe using the "20" volts setting, while the car is running alternate your AC to LO and OFF to see changes on pin 3.

3. If all is good down to the FCM input, then Test the output wires on the FCM, and if you get voltage on the orange and purple lines going to the fans then your FCM is probably good too (car running with AC on LO).

4. If all is good on the FCM output wires, then jump both fans directly to the battery to test them.

5. If these all test good, THEN i would mess with VCDS and check your coolant temperature readings to verify your lower CTS is functioning correctly. If you have a registered version of VCDS and a Ross Tech cable, then you could also try the output tests to force the fans on. The reason I suggest VCDS last is that it is not all that intuitive for this circuit, and all the physical things can be done pretty quickly and are easier for most people to attempt sans computer knowledge.