Auxiliary fan cycling on and off constantly 24/7

[beardman]

The auxiliary fan (drivers side in front of the rad) seems to always be cycling on and off. At least when the car is off, I haven't really noticed when the car is running.

Background:
2003 allroad 2.7 120K - Orig factory battery

I replaced the clutch fan with an EFK this summer, I am not sure if this is when my problem started, but at that time I also pulled the auxiliary coolant pump (under intake) and replaced that with a fitting instead.


Problem:
I didn't seem to have one until yesterday when the car seemed to take an extra few seconds to start. This morning when I went to start the car, it was completely dead, didn't even register on the dash voltmeter.

I have no problem replacing the battery (as it is orig) if necessary, but it seems that I have a bigger problem causing the dead battery anyway. Could this be the fan control module or perhaps something to do with the wiring I installed?

Thank you in advance
Joel

[alien_brain]

fan control unit?

[beardman]

fan control unit?

Maybe, but would that cause the fan to run / switch off/on all the time? Maybe my searching skills are lacking, but everything I have found leads me to believe a fcm failure causes the fan to never run or run at high speed all the time.

[4rings2turbos]

The aux pump is there to cycle coolant through the block when the car is off to help avoid heat soaking. It would make sense that it would run longer/more often since there is no cooling effect from the coolant. But after some time and the temp has dropped? It should be done running.

The combination of cold weather and the electric fan being a leach could have killed the battery. Easy enough to have it tested and confirm.

But there's still some searching to find why the electric fan is running after the engine is cooled, if that's the case. Haywire temp sensor is possible.

[beardman]

The aux pump is there to cycle coolant through the block when the car is off to help avoid heat soaking. It would make sense that it would run longer/more often since there is no cooling effect from the coolant. But after some time and the temp has dropped? It should be done running.

The combination of cold weather and the EFK being a leach could have killed the battery. Easy enough to have it tested and confirm.

But there's still some searching to find why the EFK is running after the engine is cooled, if that's the case. Haywire temp sensor is possible.

I'm sorry, it is not he EFK kit that is running when the car is off, it is only the auxiliary fan (front of radiator) that is running. I didn't really look into this in the summer/fall as it seemed plasuable to me that the fan might kick on from the sun beating down on the car. Since it is 20-30 degrees out now I can assume that this is not the case.

Is the fan control module that only thing that controls the auxiliary fan in front of e the radiator?

[4rings2turbos]

Sorry, I realized my typo and edited while you were responding.

[beardman]

Sorry, I realized my typo and edited while you were responding.

No sweat, which temp sensor are we talking about here? I have been working on multiple Audis lately and can't keep them all straight anymore. Back of the cylinder head or in the radiator hose?

[4rings2turbos]

I don't know which one would cause the issue (if it is the issue). If it were me and I hadn't replaced them since I purchased the car I might go ahead and replace both since they're quite cheap and known to go bad.

[beardman]

I don't know which one would cause the issue (if it is the issue). If it were me and I hadn't replaced them since I purchased the car I might go ahead and replace both since they're quite cheap and known to go bad.

Good call. I know I replaced on of them when I did the timing belt, I'll have to check out my records to see which one. Seems like the FCM is a PIA to replace, but for $80 maybe I'll just swap it out.

[4rings2turbos]

I know it's not really the appropriate way of diagnosing an issue, I only suggest it because of the price. Someone else may have some insight into the same issue. If the FCM is only $80 it might be worth a shot too. If you have VCDS you can see what the car say about temp (I think measuring block group 003) when the fan randomly runs while the engine is cool. You can also read the coolant temp in your climate control unit by entering the diagnostic secret menu (so very James Bond): with the key on ACC, press and hold both recirculate and the arrow up (top of dash vents), use the driver's side temp controls to cycle through channels. Press recirculate to enter and leave a specific channel to see the reading. Will need to find a list of each channel's sensor though.

[beardman]

A little more information:

I had replaced the coolant temperature sensor (green one) when I did the timing belt back in July so the auxiliary fan control sensor (blue one) has a questionable life. Also, VCDS gave me expected results measuring the temperature and my gauge has not had any issues or strange behavior.

Once I got the car charged back up, I started it up and hit the econ button as my HVAC is always left on auto normally. I was thinking that it might have a memory of sorts, but whether the econ button was enabled or disabled when the car was on does not seem to change the behavior.

It is actually both the auxiliary fan and the AC fan that are running. I tried unplugging the auxiliary fan and received the expected result in that the AC fan ran at high speed.

I did make an interesting observation that when the econ button is on, the fans are never running while the car is running (no cycling on/off). the second the ignition is turned off, the fans start up.

I will start with the auxiliary fan sensor (blue one) since I can most likely get that locally and see if that changes anything, if not I guess I'll be swapping out the FCM.

[beardman]

New Battery, fans both disconnected and blue coolant sensor on order. This should hold me over for a while.