# Radiator fan low-speed not working, high-speed is pulsing



## miknix (Jul 26, 2015)

Hello guys,

So I've been reading a lot from your forum during the past week and decided to share my findings and conclusion to check what you veteran owners think.

*Symptoms:*
- The fan slow-speed does not work (sometimes, very rarely it does).
- The fan high-speed cycles between on-off states, each lasting around 5 seconds.
- The after-run fan does not seem to work anymore.
- The AC blows waves of mostly warm but sometimes cold air.
- The coolant temperature gauge in the dashboard does not stay at 90C at all times like it used to be.. Now it stays somewhere between 70 and 90C.
- Loss of battery power to the point of not being able to startup the car.

*Conclusions*
I think the resistor inside both fans blew up (however I still do not understand why sometimes very rarely the slow-speed works on both fans, I find it hard to believe that both resistors just start working temporarily again, both at the same time).
Because the fan does not work in slow speed anymore, the coolant temperature crosses the "high-speed" threshold firing up the high-speed fans. However the high-speed fans cool it too quickly, only lasting a few seconds and then turning off. The previous cycle would then repeat giving the "on-off high-speed fan symptom".
Because the slow-speed fans do not work anymore, it messes up with the AC radiator making it work weirdly.
The coolant temperature gauge does not stay at 90C anymore because the fans are spinning too much.
Each time the "high-speed" fans fire up, they demand a high pulse of high-current (when my battery is near flat, I can see the dashboard lights dimming when the fans fire up, even when the engine is idling). I suspect that by having the high-speed fans pulsing every 10 seconds or so is demanding too much current from the alternator, leaving very few residual current to actually charge the battery.

*Questions*
- The two fans that always turn together, are they called the AC and Main fans? Where is the Auxiliary fan? Is the after-run fan the auxiliary fan or the other two?
- There is a 3-pin connector "fan switch" near the radiator (driver's side). What does this switch connect exactly? Is it between the fan control module (under the radiator) and the fan relay module (under the battery)?

*Solutions*
Given that I have indeed broken resistors in the fans, my solution is to replace the resistors with a heavy duty PWM controller externally. Something like this guys is doing:
http://www.nime.co.uk/content.php?mk4fans

I found plenty of mosfet-based PWM controllers able to switch 20A of current, it is more than enough to replace the fan stupid resistors.

I would really appreciate any feedback on this since I'm still planning what to do and how to proceed. Tomorrow I'll try to short the fan switch and check that the slow speed is indeed dead (and not the fan controller). Oh by the way, the fuse box over the battery is all clean and free of corrosion and all fuses are ok.


----------



## Hoggy (May 8, 2002)

Hi, There is no after-run fan, there is an after-run pump that pumps coolant around the turbo for 10 minutes after Ign switched off, regardless of temperature.
If thermostat working correctly, running fan will not cause low coolant temps. 
Fan control module is beneath the battery.
The thermal switch for fans is on the passenger side of radiator, on UK cars.
Hoggy.


----------



## miknix (Jul 26, 2015)

I see.. I can hear the water pump running after I turn off ignition.

So if the fans high-speed pulsing cannot cause the low coolant temperatures then I guess the thermostat switch is faulty? Damn, I guess I'll need to bring the car to the garage after all. The thermostat replacement procedure does not sound that easy to make.

Today morning I could not start the car, I had to use the jumper wires with a neighbor's car. This is starting to be a major pain in the ass.


----------



## David C (Apr 15, 2013)

The high speed fans will not be causing your flat battery.

A dead failed battery is the likely cause of that...!

Jump starting should be an emergency only route and not something you should routinely do as you can easily damage ECUs on modern cars.

The fan runs fast/stop/fast stop BECAUSE the low speed isn't working, so it is constantly on the borderline of the fan temperature switch between low speed (which are broken) and high speed.

Turn the AC off ("ECO" mode) until you fix the fans.
Actually, don't use it at all until you've fixed the fans!!


----------



## miknix (Jul 26, 2015)

Hi



David C said:


> The high speed fans will not be causing your flat battery.
> 
> A dead failed battery is the likely cause of that...!


Are you sure? The high-speed fan takes around 16 A when running nominally. At startup the fan takes a lot more than that (the high speed fuse is rated at 40 A). If the fan starts and stops every 5 seconds, there is certainly a lot of current going into those fans!
I measured the battery voltage after using jumper wires and while the alternator was spinning, it read 13.6V. Does not sound too bad for a car that has 14 years, does it?

Tomorrow I'm going to fully charge the battery using a electrical charger, then I'm going to measure the battery voltage while pulling out fuses to see if there is something sucking more than it should. My multimeter only measures up to 10 A (fused) I'm scared of putting it into series with the battery cabling.



David C said:


> Jump starting should be an emergency only route and not something you should routinely do as you can easily damage ECUs on modern cars.


It is good to know. I'm going to fully charge the battery to avoid jump starting the car again.



David C said:


> The fan runs fast/stop/fast stop BECAUSE the low speed isn't working, so it is constantly on the borderline of the fan temperature switch between low speed (which are broken) and high speed.


This makes total sense and it is what I think it is as well. However as _Hoggy_ pointed out, it does not explain the low coolant temperature visible in the dashboard (staying around 80 C)



David C said:


> Turn the AC off ("ECO" mode) until you fix the fans.
> Actually, don't use it at all until you've fixed the fans!!


Yeah, I've not been using AC at all (ouf! good thing it's a cabriolet). I'll fix the fans ASAP.


----------



## Hoggy (May 8, 2002)

Hi, 13.6 volts usually means battery is low on charge or on it's last legs.. Get it charged fully & try again.
Hoggy.


----------



## David C (Apr 15, 2013)

miknix said:


> (the high speed fuse is rated at 40 A)


I'm sure both fan fuses should be 30A.


----------



## miknix (Jul 26, 2015)

David C said:


> miknix said:
> 
> 
> > (the high speed fuse is rated at 40 A)
> ...


http://www.nime.co.uk/content.php?mk4fans

I believe you, I never actually saw the fuse, I was guiding myself based on the Golf MK4 which has similar fan wiring/controller.


----------



## miknix (Jul 26, 2015)

Important update on the issue..

Yesterday morning (after having to use the jumper cables to start the car), I drove to work and while I was driving I didn't hear any high-speed fans pulsing and the coolant temperature stabilized at 90 C! When I arrived at work, I turned on the hood and visually inspected the fans - the slow speed was working!!! Then when I saw the fans stopping, I turned on the AC and went back to check the fans - the fans were happily running in low speed and I was having cold air inside the car.
This correct behavior lasted the rest of the day, even after turning the ignition off and then restarting it again.
The good news is that this confirms that the resistors inside the fans are not damaged, the bad news is that the problem lies somewhere else, most likely the fan controller (under the radiator isn't it?) or the fan thermostat switch. Does the fan controller also control the water pump, that would explain the low coolant temperature? What about the thermostat switch, does the water pump run based on that switch?

Regarding the battery problem, yesterday I went for a 60km drive to charge up the battery a little bit, then I closed the car deactivating the alarm. This morning when I entered the car the on-board clock was synchronized by RF (I always lose the clock settings and the clock RF sync when the battery is near flat), and when I switched the ignition the ECU settings and clock were reset! It looks like the battery is in its last days. The battery looks old (the type you have to refill with water) so I'm just going to replace it with a Tudor High-performance battery (64 A/h). Any recommendations regarding the battery?
In about one hour I'm just going to measure the battery consumption of the car one hour after turning the ignition off, just to be sure it's indeed the battery and not something else sucking too much juice.


----------



## Hoggy (May 8, 2002)

Hi, Radiator fans are controlled by the thermal switch in radiator via the fan control module, beneath the battery.
After-run pump runs for 10 minutes regardless of temperature, when Ign turned off, but I believe via the Fan control module.
What's you location, I assume you are not in UK. ?
Hoggy.


----------



## David C (Apr 15, 2013)

miknix said:


> Yesterday morning (after having to use the jumper cables to start the car), I drove to work and while I was driving I didn't hear any high-speed fans pulsing and the coolant temperature stabilized at 90 C! When I arrived at work, I turned on the hood and visually inspected the fans - the slow speed was working!!! Then when I saw the fans stopping, I turned on the AC and went back to check the fans - the fans were happily running in low speed and I was having cold air inside the car.
> This correct behaviour lasted the rest of the day, even after turning the ignition off and then restarting it again.
> The good news is that this confirms that the resistors inside the fans are not damaged, the bad news is that the problem lies somewhere else, most likely the fan controller (under the radiator isn't it?) or the fan thermostat switch. Does the fan controller also control the water pump, that would explain the low coolant temperature? What about the thermostat switch, does the water pump run based on that switch?


Fan controller is under the battery tray.
After-run coolant pump is controlled by the fan controller.
The only way to get cold coolant is if the thermostat has failed & stuck open BUT it may be a faulty coolant temperature sensor. Old black sensors are a common fault. Change to revised green sensor (genuine VW/Audi only).



miknix said:


> Regarding the battery problem, yesterday I went for a 60km drive to charge up the battery a little bit...


Driving the car will do very little to charge a flat battery.
You need to take it out and charge properly (which will likely take close to 24-hours).


----------



## miknix (Jul 26, 2015)

Hoggy said:


> Hi, Radiator fans are controlled by the thermal switch in radiator via the fan control module, beneath the battery.
> After-run pump runs for 10 minutes regardless of temperature, when Ign turned off, but I believe via the Fan control module.
> What's you location, I assume you are not in UK. ?
> Hoggy.


When I left the car at an Audi garage to diagnose the problem, they asked me around 500 euros for a repair. They said the fan controller was under the radiator and was hard access (300 euros of human labor) + 200 euros of a new "controller". They also said that the car can have 2 possible controller versions and they don't know which controller it is without accessing it first.
So.. if the thermostat switch (under the radiator) directly connects to the fan controller (under the battery), what is this fan controller the garage was talking about? Were they talking about the thermostat?
I thought the fan controller (under the battery) was just a relay box with some fuses and the actual control (based on temperatures info) was located somewhere else?

So it seems the thermostat switch is at fault. Unfortunately I do not have the experience to replace it with a new one so I'm forced to go to the garage and fork some $$. :'/

Yeah, I'm unfortunately in France. It would be nice to meet you guys 

By the way, I just measured the current consumption of the car one hour after being parked, it measured around half-ampere which sounds like fine. I just ordered a new battery, I'm not even going to attempt to fully charge the old battery, I don't want it to explode inside the car.


----------



## David C (Apr 15, 2013)

miknix said:


> So.. if the thermostat switch (under the radiator) directly connects to the fan controller (under the battery), what is this fan controller the garage was talking about? Were they talking about the thermostat?
> I thought the fan controller (under the battery) was just a relay box with some fuses and the actual control (based on temperatures info) was located somewhere else?


I'll try to get a wiring diagram up for you, it makes it a lot easier to understand.
But there is a dual thermo switch on the side of the radiator. That can directly turn the low-speed fans on, even when ignition is off. It can also trigger the full-speed fans via the fan control module (under the battery tray).
The fan control module can also trigger the low-speed fans (for A/C) and also the full-speed fans.



miknix said:


> ...I'm not even going to attempt to fully charge the old battery,* I don't want it to explode inside the car*.


There are several good reasons to remove the battery from the car before charging...


----------



## miknix (Jul 26, 2015)

David C said:


> miknix said:
> 
> 
> > So.. if the thermostat switch (under the radiator) directly connects to the fan controller (under the battery), what is this fan controller the garage was talking about? Were they talking about the thermostat?
> ...


I found this one:
http://www.ttforum.co.uk/forum/viewtopic.php?f=2&t=224419



David C said:


> But there is a dual thermo switch on the side of the radiator. That can directly turn the low-speed fans on, even when ignition is off. It can also trigger the full-speed fans via the fan control module (under the battery tray).
> The fan control module can also trigger the low-speed fans (for A/C) and also the full-speed fans.
> 
> 
> ...


That's a good idea! The battery will take 48h to be delivered, I ordered it from oscaro.com don't know if you guys have that store. Even when it arrives I'm going to fully charge it using an electrical charger. So that gives me around 4 days that I'll still need to drive using the old battery.. I'm going to remove it from the car and charge it somewhere in a galaxy far far away..


----------



## miknix (Jul 26, 2015)

David C said:


> miknix said:
> 
> 
> > Yesterday morning (after having to use the jumper cables to start the car), I drove to work and while I was driving I didn't hear any high-speed fans pulsing and the coolant temperature stabilized at 90 C! When I arrived at work, I turned on the hood and visually inspected the fans - the slow speed was working!!! Then when I saw the fans stopping, I turned on the AC and went back to check the fans - the fans were happily running in low speed and I was having cold air inside the car.
> ...


Do you know where are this sensors located, are they easily accessible?
Tomorrow I'm going to visit a VW/Audi specialist, I'll keep you guys updated on what the guy says.


----------



## Hoggy (May 8, 2002)

Hi miknix, Coolant sensor.
http://www.wak-tt.com/tempsensor/tempsensor.htm
Hoggy.


----------



## miknix (Jul 26, 2015)

More updates on this..

So the new battery arrived today. I ordered it from the internet, the website where I ordered from allows you to input your license plate and then it lists all the available batteries for your car make and model. So you would suppose that the battery that arrives would be compatible and the replacement would be as simple as unscrewing some bolts, right?

Wrong! [smiley=bigcry.gif]

In fact I put the two batteries side by side, they seemed fine, same size, same structure. Then I proceeded to fit the new battery into the TT battery support and guess what??

The TT battery actually has a small cut (the battery seems to be like this, not a cut made by the manufacturer) in the bottom border of the battery, that fits in a small plastic pin in the battery support of the car!! Something like this:









Whereas my new battery is something like this:










I'm just thinking in cutting the plastic pin from the TT battery support to fit the new battery but then it makes me wonder, why is the manufacturer trying to limit the available batteries for the TT? Is the TT battery any special??
I'm also afraid that cutting the plastic away might affect the structural integrity of the battery support..

My new battery is a High Performance Tudor battery with 64 A/h of charge and 640 NE (A) of cold crank. This is more than enough for the TT I would think!


----------



## Hoggy (May 8, 2002)

Hi, Quite common to have to cut battery case, although I didn't have to on my Bosch battery.
Hoggy.


----------



## miknix (Jul 26, 2015)

Hoggy said:


> Hi, Quite common to have to cut battery case, although I didn't have to on my Bosch battery.
> Hoggy.


Yeah.. do you know if the battery will have a good fit after (not bouncing around) ? While reading around about it, it seems the TT roadster expects a shake-proof battery and now I seem to recall reading this somewhere in the engine compartment. Is your new Bosch battery shake-proof? My old battery is a Varta.


----------



## Hoggy (May 8, 2002)

Hi, I can't why a roadster requires a shake proof battery & a coupe doesn't.
Mine a 4 year warranty Bosch battery, no cutting req. on my Coupe. 
Hoggy.


----------



## miknix (Jul 26, 2015)

Hoggy said:


> Hi, I can't why a roadster requires a shake proof battery & a coupe doesn't.
> Mine a 4 year warranty Bosch battery, no cutting req. on my Coupe.
> Hoggy.


So I've been investigating a little bit more about my new battery:




























So based in this I doubt the new battery is any worse than the old battery when it comes to vibration resistance. Tomorrow I'm going to get my very sharp chisel and proceed to strip some pieces out of the battery.


----------



## Hoggy (May 8, 2002)

Hi, Most high quality batteries are built that way..
Hoggy.


----------



## miknix (Jul 26, 2015)

Alright, so the new battery is installed in the car. I really feel a difference when doing the ignition, the car starts up faster.

Trimming the new battery to fit was quite straightforward, it took me around 40 mins. First I draw the perimeter of the base of the old battery in a paper:










In the old battery, we can see some stress marks around the plastic area that fixes into the battery tray of the car:



















Then I put the new battery over the paper drawing and started trimming off plastic bits from it.. The plastic is really soft and is sliced like butter with a chisel! One must be really careful to not stick the chisel in places we do not want to cut!




























And here is the finished result, I did not trim too much to avoid damaging the structural integrity of the battery. Even so, the new battery fitted the car battery tray at the first try and with minimal effort! Here is the final result:




























I'll be removing the battery again in a half year or so, to inspect if the plastic bits attaching the battery to the battery tray aren't giving off, they seem softer than the original battery.


----------



## miknix (Jul 26, 2015)

So this morning I left the car in a Audi garage. I just received a call telling me that the "fan controller" was faulty and needed replacement. They are asking 480 euros for the controller alone, without labor.
Does anyone know what is this fan controller they are talking about? The only info I was able to find about a fan controller is regarding the "aux fan controller" which does not cost more than 100 euros.


----------



## David C (Apr 15, 2013)

miknix said:


> So this morning I left the car in a Audi garage. I just received a call telling me that the "fan controller" was faulty and needed replacement. They are asking 480 euros for the controller alone, without labor.
> Does anyone know what is this fan controller they are talking about? The only info I was able to find about a fan controller is regarding the "aux fan controller" which does not cost more than 100 euros.


The fan control module is under the battery tray.
It controls both fans.

So it is not an "aux fan controller"

Different models use different versions of the controller.


----------



## miknix (Jul 26, 2015)

Hello everybody,

Here is a quick update. I received another call from the garage, it seems they replaced the controller with a new one but the car still exhibited the same problem!!  They are putting the old controller in place again and making another diagnostic..


----------



## David C (Apr 15, 2013)

Hoggy said:


> Hi, There is no after-run fan...


Just a point on that.
It is possible for the low speed fans to run after the ignition has turned off if triggered by the rad thermal switch.
They won't automatically run like the after-run pump does, but they may do if the temperature is high.


----------



## miknix (Jul 26, 2015)

David C said:


> Hoggy said:
> 
> 
> > Hi, There is no after-run fan...
> ...


I thought so! I remember hearing the fans still spinning even after I exited the car and closed it down. That is, before I had the problem explained in the thread.


----------



## miknix (Jul 26, 2015)

So I have the car back from the garage. The car was one week there, the guys first replaced the fan controller, but the car was still showing the same problem so they put back the old controller. Because they only charge for successful repairs, I was not charged for it. Then they proceeded to replace the fan thermostat, which didn't solve the problem either.. They told me they left the new thermostat in the car and they were not charging for it.
I'll return the car to the garage again later this month to make another "diagnosis", I need the car for now.

From all of this I learned that this particular Audi garage is very recommendable, they might be expensive but they seem to be honest with their customers.


----------



## silkman (Jul 29, 2004)

Hi, I have the same problem as you do, the circulator pump is working when engine is off but it overheats (temp goes well above 90C up to 115C sometimes) when i turn it off. Gonna change the fan controller and the dual thermoswitch.

Low fan speed almost never works, high speed is working fine.

FYI, the fan controller is expensive from audi (about 181€ from Germany) but there are many to be found on ebay about 50€. The dual thermoswitch is about 32€.


----------



## Hoggy (May 8, 2002)

Hi, Coolant temp on a Hot engine will always rise when engine is shut down. There is a tremendous amount of under bonnet heat on a turbo engine & the heat sink effect with no airflow through rad will cause coolant temp to rise.
Have you ever lifted the bonnet after a good run ?.. [smiley=devil.gif] 
Nothing to worry about as long as coolant temps are controlled when engine running.
Hoggy.


----------



## Jez xbx (Oct 24, 2014)

silkman said:


> Hi, I have the same problem as you do, the circulator pump is working when engine is off but it overheats (temp goes well above 90C up to 115C sometimes) when i turn it off. Gonna change the fan controller and the dual thermoswitch.
> 
> Low fan speed almost never works, high speed is working fine.
> 
> FYI, the fan controller is expensive from audi (about 181€ from Germany) but there are many to be found on ebay about 50€. The dual thermoswitch is about 32€.


I might be miles off target but......
I'm assuming you can hear the pump running when you switch off the ignition?
Yet the temperature climbs significantly?
So is it possibly the after run pump is not in fact pumping any fluid?
IE the motor is running, but the pump is not pumping???


----------



## Hoggy (May 8, 2002)

Hi, The after-run coolant pump is there to cool the turbo bearings, not to lower the coolant temp.
Pump can pump as much coolant as it likes but without an airflow through rad coolant temp will not reduce.
As I said coolant will rise on a stationary hot engine.
Hoggy.


----------



## David C (Apr 15, 2013)

Hoggy said:


> Hi, The after-run coolant pump is there to cool the turbo bearings, not to lower the coolant temp.
> Pump can pump as much coolant as it likes but without an airflow through rad coolant temp will not reduce.
> As I said coolant will rise on a stationary hot engine.
> Hoggy.


The V6 has an after run pump too, so it isn't just about turbo bearings and if the temperature rises to the low speed fan trigger temperature the fan will run.


----------



## rodhotter (Dec 30, 2011)

the fans sequences are surely complicated to say the least! my 2001 225Q was having fan issues, a $50 scan from a close vw-audi-porsche tuner garage confirmed the fan controller. got one on line for about $150, installed myself in an hour, not hard just remove battery + tray + there it is!! a service manual is a good help as these great forums are. i am USA but this forum is best with owners like WAK a great source of info!!!


----------



## miknix (Jul 26, 2015)

Hello guys, I am sorry for the late reply. Regarding the problem described in the thread, I ended replacing the fans, the thermoswitch and the water pump. Because the water pump is usually replaced at the same time as the timing belt, I ended up replacing that as well (the timing belt was due in 1 year). The replacement was done by Audi and led to a quite exorbitant bill! At least I now have two years of warranty on the engine cooling system and timing belt which is nice.. I was also told that my dashboard has a 5deg (C) error on the shown coolant temperature but it doesn't affect operating.

Meanwhile I've come to meet a guy that used to work for WV and now has his own small garage (franchise of a ECU reprogramming and tuning chain). This guy is very honest and takes the time to explain to me how things work and what to look for.. I surely won't be bring my car to Audi again.


----------

