# Dumb Cooling Fan question, No After-Run, Fans only run with A/C on



## beetlevdubn (Apr 25, 2005)

I know that there have been a ton of issues related to the fans, so I have been doing a ton of searching and reading about the low speed fan resistor issues. The one thing that I haven't been able to identify, is which fan is the low speed fan and which typically runs after the engine is shut off and the car is at operating temperature? Is it the smaller fan on the pass side, or the larger fan on drivers side? I am pretty sure that my low speed operation is toast, as I get no after-run fans at all, and the only way I can get the fans to come on, is by turning the A/C on. 

I started with the fan switch on the radiator, same issue. Then I swapped out the fan control module, same issue. Then I swapped out the Coolant Temperature Sensor, with a new green top sensor, same issue. 

The whole time, I think back, and I have only heard the high speed operation of both fans together, and never had the fans come on after the car is turned off (even in 94 degree heat). 

So, I am pretty sure that my low speed fan (I think its the smaller fan on the pass side of the car), has the dreaded resistor issue, which is causing no low-speed operation. 

If anyone can help me identify which fan it is, that would help tremendously.


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## TTBodie (Aug 1, 2011)

My small fan (V177) starts around 92C with (V7) kicking in around 103 with A/C off. With A/C on V7 is on full time I think somewhere below 35 mph no way to know for sure. I don't know about the resistor issue, I do know if the fan motor is open circuit it's toast, verified on my V7. Does the small fan run with A/C on? With everything you've swapped out I'm thinking maybe wiring. I'd get a vag scan.


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## beetlevdubn (Apr 25, 2005)

Yea, both fans spin, but it appears that they are both just running at high speed all the time when the A/C is on. I have a VAG-COM and there are no codes at all, and the temps show that it gets up to 100 and no fans without the A/C on, but it never gets much higher than 103. 

I am going to run the voltage test on the fan switch plug, jump pin 1 to 2 should be low speed, and jump pin 2 to 3 for high speed. I will check tonight, but I am guessing that the fans will not spin duing low speed test.


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## beetlevdubn (Apr 25, 2005)

So, I used the following graphic to do my test: 










I jumpered from pin 1 to 2 (low speed operation), and the fans both came on in low speed. 

Then I jumpered from pins 2 to 3 (high speed operation), and nothing. I checked the source voltage at pin 2, and sure enough, 12.6v, but when I jumpered over to pin 3, there is nothing... no sparks, no humming, no heat in the jumper wire, nothing. So, I am not sure what that means. If I had day light, I could have disconnected the fans at the plugs on the bottom of the shroud, and checked to see if I still had 12.6v to each fan, then jump 12v and ground to each fan, but since there are three wires, not sure which is high speed, and which is low for each fan. Maybe someone has a schematic of the wiring to each of the fans from the plugs.


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## beetlevdubn (Apr 25, 2005)

Anyone?


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## TTBodie (Aug 1, 2011)

Don't have a schematic to send but from the coolant fan control module (J293) both fans motors are powered by red and black, the fan speed resistors are powered by red and white shared between V7, V177 and F54 ( half of the fan control thermal switch). Brown and black are grounds. The red and yellow from J293 is switched through F18 ( the other half of fan control thermal switch) and connects to the A/C wiring harness which I'm guessing switches on V7 when A/C is selected. 
Hope this helps.


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## beetlevdubn (Apr 25, 2005)

Thanks... where are you getting the information? I assume the Bentley? If so, does it describe the operation of the fans under certain conditions? It appears that when I turn the A/C on, the fans are just on low speed. I can't get high speed to come on at all, so not sure where to really check. I'll split the two plugs at the radiator shroud tomorrow, and see if I can get either fan to go into high speed.


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## TTBodie (Aug 1, 2011)

Yes it is from the bentley service manual, unfortunately it doesn't go into any detail, all I can tell you is my fans go to high speed anytime 49C says it's over 105C and high speed usually only is on less than a min before the temp lowers, mostly at stop lights and slow speeds. The Audi repair manual prob is more help as far as how it's supposed to work. 
Maybe a vag scan can help. Gotta say too I've bought brand new bad elec stuff before!


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## beetlevdubn (Apr 25, 2005)

Ok, so to update this thread, it looks like we have narrowed it down to a couple things. Remember, the symptoms are, no fans without turning the A/C on, and no after-run of the fans at all.

So, I disconnected the fans at their plugs, and gave them power and ground, and both fans spun at low speed, and at high speed, no issues at all.

Then, I removed the thermostat, and it was in fact, stuck open, so I swapped the thermostat out. More on this later....

Then I tried to jump the radiator switch plug, from 1 to 2, and I got low speed fans, then tried to jump 2 to 3, which I was told, should be high speed fans, but I got nothing.

So, now I fired the car up, connected VAG-COM, and watched 004 measuring block, which shows the Coolant Temp Sensor. CTS got up to 102 degrees Celsius (220 degrees farenheit), and no fans, nothing. The car gets up to temp faster now that I have a working thermostat, but it also creates a scary situation without the fans working properly.

Since nothing has gotten me closer to fixing the issue, now I start to suspect the new fans switch that I just replaced, could it be a bad new part, and also the fan control module that I just replaced?

So I decided to test out the radiator temp sensor/switch, which should get continuity at 95 degrees celsius for low speeds, and 102 for high speed. I connected test wires to the low and high speed terminals of the switch, fired the car up, and watched my meter as the car warmed up and also watched the coolant temp sensor via VAG-CAM. The CTS went all the way to 103, and no continuity from the switch. So, I got another new switch installed, and we got the same results. Swapped the fan control module with another new one... and same thing.

I pulled the battery tray out, checked all of the grounds, etc. and everything looked perfect.

I pulled one of the fuses in the panel on top of the battery, and there was a bit of melted plastic, so I figured, maybe that was the issue, as a number of people have had those go bad. Swapped that panel out... same thing.

So, the final test that really narrowed it down, was that we took the old radiator switch, plugged it into the harness (without it installed in the radiator), used a lighter and got the sensor really hot. Once we did this, the fans finally came on. This shows that the wiring is actually fine.

Now, back to my thermostat swap I did earlier... if I was thinking, I would have stuck my finger in where the water pump was located, and checked to see if the impellor is rotating on the shaft. My bets are now, that the water pump was not replaced when the timing belt was done only 10K miles ago, by to the Jerry-Rigging idiot of a previous owner, or that the radiator is plugged not allowing warm water to reach the fan switch.

So, next week, we will be checking the water pump first, and if it looks good, we will swap the radiator next. What a royal pain in the butt, but it looks like the problem is finally fixed. I'll post back next week after I replace those pieces.

Thanks for all of the help...


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## beetlevdubn (Apr 25, 2005)

Well, have you changed your radiator yet? Also, mine overheats very quickly now, so in my mind it could be either, and its easy to check the water pump by removing the thermostat again. I can't even tell if the impellor is plastic or steel until I check... if its plastic, I'll swap the water pump either way.


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## beetlevdubn (Apr 25, 2005)

Well, you were right... my water pump was fine...

I pulled the water pump, just to check its condition, and to see if it had a plastic or metal impellor, as the previous owner had replaced it, but his other work on the car was half-assed at best. So, after doing all of that, I was able to determine that it did in fact have a metal impellor, and it looked to be new. So, no issues there. I guess I get another new Timing Belt even though the old one was only 15K miles old.

So, I am left with replacing the radiator, which I will be doing this week. At this point, it has to be that. I checked the switch and wiring, by leaving the switch connected to the plug, using a cigarette lighter and heated it up, and the low speed fans came on. I couldn't check the high speed operation this way, as I burned my fingers trying to hold the lighter for as long as I did waiting for the switch to heat up to low speed.

The other tell-tale sign for us, the lower hose gets warm, and the upper one gets real hot. As far as I can tell, the lower should be hotter, as it is the water that comes straight from the engine/thermostat. If the radiator is plugged, which I think mine is, then the lower should be warm to hot, and the upper should be cooler after the coolant has gone through the radiator. I believe the flow is as follows:
Water pump -> Thermostat -> lower hose -> Lower inlet of radiator -> Outlet of radiator/upper hose -> Side of head/heater core -> Engine/waterpump


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## liloldbie (Jun 23, 2007)

Watching! I am in the same boat. My lower hose is barely warm as well and my upper is dead hot. I am down to the final step as you are by replacing the radiator. Let me know if that works for you.


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## beetlevdubn (Apr 25, 2005)

Well, as it turns out, I had the coolant flow backwards, it actually pumps through the head, then out the upper hose, then into the radiator, then to the thermostat and back to the pump. Regardless, if the radiator is plugged, not much water will be making it through, and if the plug is anywhere around the coolant fan switch, then it is preventing hot water from getting to the switch itself.

Another symptom... there doesn't appear to be a lot of flow to the coolant bottle, and when I remove the coolant bottle lid, I get no release of pressure and the water isn't super hot.

The coolant bottle and lid have been replaced as well (they are brand new), and we used a commercial coolant tester and verified that the coolant system is sealed, and holds more than the 22psi that its rated at.

One other thing that makes my situation a little different, is that I bought the car with the front end off after a small accident that damaged the bumper, radiator and condensor. I bought the car with replacement parts provided by the guy I bought it from. The radiator was used, and was thicker than the radiator that normally comes on our cars. Almost like a 3 or 4 core vs. the standard 2 core that I have typically seen. Everything mounted without issue, so I never gave it any other thought. Regardless, it looked like it had a lot of miles on it, so I am hoping that replacing it with the correct radiator that is new, will fix the issue.

I'll know more this week and update the thread with the results.


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## beetlevdubn (Apr 25, 2005)

So, today we figured out the issue, and it was a complete surpise to me. It goes back to the radiator I described in the post above. It fit my car perfectly, and I assumed it to be the correct radiator for the car. Today, we pulled this radiator, and I broke each of the end tanks off, and the radiator looks perfectly clear, no blockage, no issues at all.

We replaced this radiator (that looks like a 3 core), with the stock 1 core radiator, and the system works perfectly. I am guessing that the radiator was from some other Audi, either a V6 or even possibly a V8 car (like a B6 S4) or something similar, and the small water pump that our cars have, didn't push enough volume to get the hot water circulated to the fan switch.

So, the lesson learned is, make sure you know what parts you are getting if you are getting used parts, and in my opinion, don't ever run one of the 3 core radiators that I have seen advertised.


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## GTITDub (May 20, 2005)

Very good information for me to check. Only thing I have an issue with is that my after run fan stopped working after I change my alternator and the car will overheat while driving. Temp never goes above the mark between top middle and 230 on my gauge. I tried jumping #1 and #2 and my low speed fans come on, but when I jump #2 and #3, no high speed...(Checks with and without the ignition being on) What would you suggest?

Thanks, 
Nick


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## beetlevdubn (Apr 25, 2005)

How are you checking your temp when you see the 230 degrees? My after run fan never comes on, and my gauge never moves. Usually the only time I have heard the after run fans come on is when its like 90+ degrees outside.

I ran the same test you ran, and only got low fans as well, I don't think you can get fans to come on when you move the jumper only... because the circuit goes through the fan control module for high speed, but I am just speculating.

The high speeds are supposed to come on at 105 degrees celsius, I believe, which is 221 fahrenheit


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## GTITDub (May 20, 2005)

I am just looking at the temp gauge on the instrument cluster. Normally is is sitting top center but when this problem occurs, it goes to just left of the mark before the 230 mark. Kind of confusing how it sounds, but I can't find a picture on the web to show you what I mean. Im in Alabama, so it hasn't gone down below 90's yet except this week. Just started noticing it after I changed the alternator which was this past weekend. Haven't had hot enough weather to see if high speed comes on. Maybe I am just being paranoid, but I like seeing the temp gauge not move after it is at operating temp  If all else fails and it keeps doing it, I will just replace all the cooling/radiator items when I do the turbo install next year since the engine has 130k+ miles on it. I would just hate for something to happen since my MKIV's slave cylinder went out a couple weeks ago. 

Other than my rambling on, you think I should start at the fan switch? Or the FCM?

Edit: Just realized this was an Audi TT post  Im in a MKIII vr6 GTI if that helps any


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## Vstone2262 (Mar 4, 2010)

^ I have the same issue.

A green coolant temp sensor seemed to help but it does the same thing now. Im guessing my tstat is stuck or something is not flowing correctly. I have a small coolant leak under the sensor as well.


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## beetlevdubn (Apr 25, 2005)

Well, the gauge gets its input from the CTS, and the fans get theirs from the fan switch. So, there is a chance that your thermostat is stuck, causing the CTS to read high (230), and by the time it goes through the radiator, to the fan switch, the coolant has cooled down, so the after run fans aren't running.

I would lean towards the cheap/easy fixes first, you can do a fan switch, cts, and thermostat, for about $40 or so. Usually the Fan module goes bad by allowing the fans to run constantly (with ignition off), or they never come on at all.


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## GTITDub (May 20, 2005)

Ok, good deal! I will start from there and see how it goes. Thanks for the help!

Nick


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## ellayyo8 (Aug 29, 2012)

*just joining in to beetle...*

After having looked at all your posts..just couldnt wait to see if there was a link between yours issues and mine..well you see i have a 2000 audi tt and just had a problem with my larger fan burning out and had both fans replaced just to be on the safe side and well now they both work on high speed but havent seen them run on lower speed. Plus my fans both kick in at 100 celcius thru the vag 49 test on the display screen..you keep on saying that the lower speed should kick in at 95 degrees and fast at 103 but mine only kick in once and thats at 100 every time only staying on for maybe a couple seconds untill temp falls to 98 celcius and then the process starts again untill it heats up.so im gessing either my car doesnt have two fan speeds or the low speed is busted.thos would be the first of my problems...the second one is that now as soon as i turn the ac on the fans kick in and stay on for about a minute and then they turn of and i get hot air as well as getting a lot of pressure on the compressor since the condensor is getting hotter from the fans not being on...i really apreciate some feedback guys..


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## AudiTT2Q (Sep 1, 2012)

*ellayyo8 A/C blows hot air*

Hi,

Your post is a bit old so maybe this does not help. 

Anyway if the A/C kicks in and then stops it could be because you do not have enough Refrigriant pressure in the system.

There is a pressure sender in the upper left corner of the engine compartment just below the cross bar. This sensor has two functions, It will stop the A/C both if the pressure is too low or too high. This sensor does not allow the A/C to run if either situation exists and possibly it shuts down the A/C and fans automatically after being on for a few seconds.

So for your issue I would have the refrigriant level checked by a pro to see if that helps. If the pressure in the system is OK then the sensor could be defective.

Regards AudiTT2Q


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## lite1979 (Sep 9, 2005)

ellay08, i would check the fuse tray on top of the battery in your car. The fans depend on some of these fuses to operate normally, and because of the design of the tray and how often the radiator fans get used in our cars, it's not uncommon for the tray to melt, causing the contacts for the fuses to spread and interrupt the circuit that keeps your fans on. The fuses may be (and probably are) fine, but where they sit may not be making contact all the time. I also agree it's time to start a new thread on this.


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## ellayyo8 (Aug 29, 2012)

*fan speeds on 2000 tt*

Hey do any of you know if the fans have two speeds and if they do when should the faster speed kick in? Im thinking my faster speed is not engaging!! The car gets to 97 degrees and the fans come on snd then turn if when the car cools down never reaching the 100s, now when the AC is on the fsns come on which is normal but then the faster speed on the fan doesnt ever come on....im thinking that it used to come on before!!! Its getting colder down here in California and maybe thats why they are not coming on..dont know can anybody help??


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## lite1979 (Sep 9, 2005)

I believe the larger of the two fans has two speeds, but it's more likely the slower speed is not engaging if you can only make the fans turn on with the A/C. Did you check your fuse tray on top of the battery yet? For simplicity's sake, I would start a new thread that clearly defines your problem and leave this thread to the archives.


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## motorlager (Sep 26, 2005)

Hey guys, i noticed your cooling system whoes, so as a recent TT 225 owner and audi tech i thought i could shed some light on the subject as best i can. 

Both cooling fans have 2 speeds. low comes on around 95 and around 100 for speed 2 give or take a few degrees. 

If you have a working a/c system- low speeds should be on all the time the a/c is on. If not, the a/c clutch will cycle on and off continually due to high pressure which is detected by the a/c pressure switch. 

The a/c pressure switch can detect too low or too high of pressure and will cause the fan module (fan and a/c module combined) to disengage the a/c clutch. 

If low speeds are inop with the a/c on, your battery fuse bracket could be burned up *or* the low speed is burned out in the fan itself. I see mostly burned out low speed fans. Its not uncommon to find both fans are burned out on low speed but the high speed still works. In this case the a/c clutch will be engaged and the fan(s) will cycle on and off. 

There are many other situations as well on these cars such as a bad water pump or thermostat, radiator, fan module etc... But first turn on the a/c and pop the hood. If the a/c compressor clutch is spinning, both fans should be turning on low speed (very hard to hear, quiet on speed 1) so look at the fans. On very hot days its not uncommon to hear the fans alternate between 1 and 2, especially with the a/c on. 

Hope it helps  And hello! Noob to the TT forum.


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## XXX 1.8T (Aug 10, 2002)

Guys stupid question but since i have changed my water pump and done timing belt my car when idling in traffic goes to 95 and then back to 90.

is this normal because i dont remember it doing it as much?

I tested the AC and both fans run so temp stays at 90.

Ive also checked the thermostat and this is fine.

I read somewhere if you get a cooler thermostat you can make an adjustment in Vag Com for the fans to kick in earlier? Or do i have my info wrong?


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## lite1979 (Sep 9, 2005)

Please start a new thread specific to your problem. This thread is over a year old and has nothing to do with your situation.


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