# Cooling fan problem - diagnostic logic review needed.



## john_kattenhorn (Jun 21, 2014)

Hi All,

I was wondering if someone who has had and resolved the cooling fans not working on their TT could follow my diagnostic path and suggest where I might have gone wrong ?

Problem

MOT Centre said that car was overheating so wouldn't test it. I've left it running for an hour and it never got beyond 90 BUT the fans never came on, I read that with the aircon on the small fan should always be running and I can hear the electric pump running when the car is first switched off.

Diagnostics

I checked the fuses on the top of the battery and no. 16 and they were good.

I un-plugged both the fans and applied 12v to them and they both span, didn't know about fan speeds at this point so didn't try both speeds though.

I took out fuse 16 and neither fan came on.

I un-plugged the radiator sensor (once I'd found it) and tried shorting from 2 - 4 and 1 - 3 but made no difference.

I then took out the battery out to get to the fan control unit and discovered that the battery tray had cut through the red wire leading to the plug on the top of the battery marked '3'. I repaired the wire, still no joy.

I disconnected the old fan control unit and plugged in a new one I got from GSF, still no joy.

I removed fuse 16 and both the fans came on. Putting back the fuse the fans stop.

I changed the control unit back to the old one and removed fuse 16 and both fans came on. Putting back the fuse the fans stop.

So I'm thinking the only part I've not tried is the temperature sensor but before I go spending any more money I was wondering if there is any more tests anyone could suggest to narrow down the problem ?

Thanks in advance

John


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## john_kattenhorn (Jun 21, 2014)

Update:

Checked the voltage coming out of the fuse box above the battery and all was good.

So I then removed the coolant sensor lead from the sensor and the shorted between connectors marked 3 and 1 and fans burst into life.

So I think it's the sensor, I'll get a new one tomorrow. Means I've got a fan control unit which I don't need I suspect but that can go in the spares cupboard


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## Hoggy (May 8, 2002)

Hi, Coolant fans will not run until coolant temp (Code 49c) reaches 98/100 ish. 
Coolant temp sensor Code 49c has no connection to fan cut-ins, so do you mean shorting thermal switch in Rad causes fan to run.
Hoggy.


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## john_kattenhorn (Jun 21, 2014)

Hi Hoggy,

Thanks for the reply; strange I could have sworn both fans cut in (I was aware that the aircon fan should be going at all times) unless Econo is switched on. The rad fan definitely did though, got my girlfriend to take a look at the dash whilst I was shorting the connections and she said temp gauge went straight to red and the symbol for over heat appeared which I sort of expected.

The problem I had that even before I found the broken wire the car never overheated when I drove it (pretty hard too) and left it to idle, yet the MOT centre threw the car straight back at me saying it was over heating and dumping coolant which neither of us have seen.

Maybe I'll just change the sensor and take it back and see what happens.

Does pulling the fuse normally indicate a bad fan control unit ? Could I have got a bad one from GSF as well which is throwing out my logic ?

Thanks

John


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## Hoggy (May 8, 2002)

Hi, It's possible fan control is duff, but high temp indication from coolant sensor will not cause fans to to run,
Fans are started from thermal switch in Rad via control module.
Fuse 16 failed or pulled will cause fans to run, so it appears fan motors are O.K.
Hoggy.


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## john_kattenhorn (Jun 21, 2014)

Hi Hoggy,

I'd read about a sensor in the radiator too about 1/2 down on the passenger side but I've got nothing, no sensors that I could find down either side. I've only just put all of the bumper etc. back on so I really didn't want to take it all apart again.

I'm wondering what I actually did by shorting those two connectors marked 3 and 1, it's definitely kicked in the fans and I did it a couple of times too.

I starting to wonder exactly what my girlfriend as got here now 

Thanks

John


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## Hoggy (May 8, 2002)

Hi John, Even stranger if you have no thermal switch in radiator, as that's where it is... 2/3rds way down passenger side.
Hoggy.


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## john_kattenhorn (Jun 21, 2014)

I'm going to check again, it must be there surely, presumably easier to see from underneath right ?

Thanks

John


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## sco (Mar 2, 2013)

John,

Not sure where you are in Northampton but if you are looking for a no nonsense MOT I can thoroughly recommend Johns Motors in Fosters Booth on the A5.

Simon.


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## john_kattenhorn (Jun 21, 2014)

Hi Sco,

Thanks for that, I think I know where you mean as I used to live in Bugbrooke, I'll look them up.

Cheers

John


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## sco (Mar 2, 2013)

Yep 5 minutes from Bugbrooke - I'm in Nether Heyford.


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## john_kattenhorn (Jun 21, 2014)

Hi,

UPDATE: So I've located (Thanks Hoggy!) and replaced the Fan Temperature Sensor on the Radiator and it's still the same. The fans only run if I remove Fuse 16 and no matter how long I leave it running (even in this hot weather I can't get the needle to pass 90, but no fans in any case.

So I've now changed:

Fan Temperature Sensor.
Fan Control Unit
Fuses in holders above battery.

I've also :

Fixed the damaged wiring from the Fuse Holder above the battery into the loom.
Cleaned the Fuse Holder Sockets.

Anyone got any ideas I should try ?

Thanks

John


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## Hoggy (May 8, 2002)

Hi John, surprised coolant temp won't rise above 90. Fans won't cut-in until 100+ ish any way.
Next time engine warm/hot, aircon off, hold revs at 1700 ish, coolant temp must rise to 100+ & then see when/if fans cut-in. 
Hoggy.


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## john_kattenhorn (Jun 21, 2014)

Hi Hoggy,

Will do, am I right in thinking that the aircon fan should run at any temp so long as ECONO is not selected ? When I checked the fans I'm wondering if I only applied 12v to the high speed and maybe both the low-speed are shot, same when Fuse 16 is pulled ?

I've give your test I tryout when I get back home next weekend and let you know.

Thanks for sticking with me on this 

John


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## Hoggy (May 8, 2002)

Hi Just leave air con off, left hand switch/knob not pushed in & fan shouldn't run. If you want to monitor Code 49c (actual coolant temp) without aircon on, push econ button in.
Hoggy.


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## john_kattenhorn (Jun 21, 2014)

Hi,

UPDATE: Fans are now working, but still no sure what was going on.

I re-assembled the battery try, re-mounted fan heating control unit etc. and performed the test as Hoggy suggested this weekend and when I got back sure enough the fans were seemed to be working normally starting and stopping as the temperature gauge moved over the 90 and back again.

The thing which still bugs me is that the ac fan still does not run on start-up as other way suggested if it ac is running.

It's passed the MOT though so the girlfriends happy and we are off to Audi's in the Park in Northampton therefore I can go back to working on other things.

Thanks for everyone's help.

John


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## BadgerTT (Nov 16, 2019)

Have noticed that my main radiator fan may not be kicking in after being sat idling for a while and showing fully up to temp on guage (need to check against 49c to verify), but in this thread it mentions pulling fuse 16 to see if the fans start, so just wanted to check the location of 16 - is it one of the three 30a fuses on top of the battery (as handbook as 16 in the side panel as something different)? Is the control module under the battery? And I presume it is coolant drain to change the temp sensor in the radiator if it comes to that?


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## davebowk (Aug 16, 2019)

Right side of the dash fuse panel, 10 amp fuse top one second from left. RHD car. It is number 16 that will turn the fans on with ignition on when removed.
Just fitted a replacement big fan this weekend so fresh in my head.


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## Hoggy (May 8, 2002)

Hi BadgerTT, Do the fans run if A/C is ON?
Also check the cooling fan fuses on top of the battery.








Both fans should always run at the same time. 98 degrees ish both on slow speed, 106ish both on high speed. 
The thermal switch in rad will require a coolant drain, but changing the coolant temp sensor (Code 49) will only lose a small amount of coolant.
Hoggy.


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## BadgerTT (Nov 16, 2019)

So only the small fan runs, big one is stationary. So I need to test if it runs I guess through the fuse 16 pull option. If it makes no difference fan control unit or fan itself as the next step? Green 30A fuse looks ok.


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## David C (Apr 15, 2013)

BadgerTT said:


> So only the small fan runs, big one is stationary. So I need to test if it runs I guess through the fuse 16 pull option. If it makes no difference fan control unit or fan itself as the next step? Green 30A fuse looks ok.


Fans are wired as a pair.
They can only run as a pair.

If only one fan runs, the other one has failed.


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## BadgerTT (Nov 16, 2019)

Davebowk - thank you for the steer onto the fuse, will check later to confirm just the small fan is working. Looks like I might be heading for a fan replacement, any top tips for the swap out? Think you might have mentioned somewhere about needing to take the throttle body off?


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## davebowk (Aug 16, 2019)

BadgerTT said:


> Davebowk - thank you for the steer onto the fuse, will check later to confirm just the small fan is working. Looks like I might be heading for a fan replacement, any top tips for the swap out? Think you might have mentioned somewhere about needing to take the throttle body off?


You need to get underneath for the fan frame bottom screw and the wiring connector.
Remove top plastic trim panels
Undo top 2 screws and remove throttle body
Then you need to get it past the aircon pipe and the rad top hose.
I had to get the support arms in a position that rotating them forced them past the pipes.
It's tight but doable.
If you remove the rad top hose it will come out easier but then you have coolant loss.
When free remember the orientation as it came out and refit in reverse.

I replaced it with a A3 fan i think. The motor is a bit smaller depth wise. It was flush with the back of the support frame


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## BadgerTT (Nov 16, 2019)

Great, thank you. Found a couple of videos showing swaps in Golfs, just don't have the throttle body in the way. Checked the fans for free spinning and the big one has a fair degree of resistance so looks like it is goosed, ordering a new one (need to check diameter) - though a suprising difference in prices between GSF and ECP. Necessary to renew the throttle body gasket? Another unexpected task in life with a TT.


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## davebowk (Aug 16, 2019)

BadgerTT said:


> Great, thank you. Found a couple of videos showing swaps in Golfs, just don't have the throttle body in the way. Checked the fans for free spinning and the big one has a fair degree of resistance so looks like it is goosed, ordering a new one (need to check diameter) - though a suprising difference in prices between GSF and ECP. Necessary to renew the throttle body gasket? Another unexpected task in life with a TT.


Yeah, new gasket required. I have gasket material so just made one.


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## tt92103 (Jun 4, 2015)

Consider unplugging the fan connector and applying 12V to it to make sure it is dead, before going to all the work of removing it. It is a 3 pin connector. The wire colors are Brown (GND), Red/White (low speed), and Red/Black (high speed).
On low speed the current flows through a resistor (1 ohm i think?).


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## dlk1231 (Jul 30, 2018)

My car runs very hot, thought I had oil leaking on to manifold as light blue smoke coming from engine bay when hot, no oil leaks but found both fans not kicking in, they seem seized as cannot turn them easily by hand, took fuse 16 out but still not on, fuse on battery is fine, tries AC Auto. Any tips on un-seizing fans?


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## David C (Apr 15, 2013)

[email protected] said:


> My car runs very hot, thought I had oil leaking on to manifold as light blue smoke coming from engine bay when hot, no oil leaks but found both fans not kicking in, they seem seized as cannot turn them easily by hand, took fuse 16 out but still not on, fuse on battery is fine, tries AC Auto. Any tips on un-seizing fans?


I'd buy a new pair of fans.


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## BadgerTT (Nov 16, 2019)

Main fan replaced and now done the Fuse 16 pull test but still no main fan (smaller Aircon fan running as expected ( stopped when AC off and running when on). Fuse on top of battery must be fine as power to AC fan, so is the fan control unit the next logical thing to swap out? Old main fan was fairly stiff to rotate so a possible I guess that has messed up the control unit. Can the control unit be tested (don't have VAGCOM yet)?


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## Hoggy (May 8, 2002)

BadgerTT said:


> Main fan replaced and now done the Fuse 16 pull test but still no main fan (smaller Aircon fan running as expected ( stopped when AC off and running when on). Fuse on top of battery must be fine as power to AC fan, so is the fan control unit the next logical thing to swap out? Old main fan was fairly stiff to rotate so a possible I guess that has messed up the control unit. Can the control unit be tested (don't have VAGCOM yet)?


Hi, Have you checked/cleaned up both fuses on top of battery?
Hoggy.


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## David C (Apr 15, 2013)

BadgerTT said:


> Main fan replaced and now done the Fuse 16 pull test but still no main fan (smaller Aircon fan running as expected ( stopped when AC off and running when on). Fuse on top of battery must be fine as power to AC fan, so is the fan control unit the next logical thing to swap out? Old main fan was fairly stiff to rotate so a possible I guess that has messed up the control unit. Can the control unit be tested (don't have VAGCOM yet)?


It isn't an "AC fan" and a "main fan"
It is two fans wired as a pair.

Both run together either at low speed or full speed.

Both should run constantly when AC is on.

So it points to a failed big fan or a wiring issue to that fan.


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## davebowk (Aug 16, 2019)

I replaced the fan control unit first thinking it was that from the start but it was my fan.
Got a cheap pattern one from ebay.

Did you test the new fan before fitting?


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