# '03 TT: What triggers the high speed fan?



## CageyBee (Jun 15, 2000)

*Fixed - solution below:*

Hi all, I've been suffering with this annoying problem for well over a year now.

Basically, the high speed fan will turn on within a few minutes of the car running and the car thinks it's overheating. Without rehashing the entire story, I'm curious if there is a list of items that can trip the high speed fan.

I've replaced:

Thermostat, green coolant temp sensor and the rad fan switch. Anything else come to mind?

It's an '03 TT roadster 1.8t 180hp, 6speed automatic.

Thanks in advance!

Danny


----------



## Doooglasss (Aug 28, 2009)

Did ya replace the Fan Control Module ?


----------



## CageyBee (Jun 15, 2000)

DougLoBue said:


> Did ya replace the Fan Control Module ?


Thank you, yes I did albeit it was a few years ago.

However the cluster suggests the temp is way high too which makes me wonder if the FCM is able to send data to the cluster, in addition to triggering the fan on to high---?

It's all such a mystery.

I'm curious too if a bad instrument cluster can trigger the high speed fan to come on. I don't want to buy a $1400 cluster just to find out.


----------



## Doooglasss (Aug 28, 2009)

You can test your cluster in vagcom under instrument cluster. Make sure the gauge is working properly. Also check your coolant temps with vagcom as well?


----------



## Cabbet (Nov 25, 2007)

Compare the coolant temp and engine temp with your guage using your heater controls to go see data if you don't have vagcom


----------



## J Patterson (Apr 11, 2009)

*Things that make high speed fan come on---*

1. 105C coolant temp
2. AC on

If your gauge is reading high, check it with the HVAC display block 49

(recirc button and UP arrow at the same time IIRC )

The gauge is not linear in response. It will read centered from about 85C up to 101C at which temp it will move up one mark on the dial.

If the Hi Speed fan does not run with the AC on, suspect the fan motor or the Fan Control Module.
You can check the fan motor with a jumper wire.

Good luck. FWIW it is common for the gauge to read wrong in the cluster and give a false hot indication.


----------



## CageyBee (Jun 15, 2000)

Thanks all for your insight---I should have mentioned I've been over and over and over and over this a hundred times.

Basically 49C shows crazy values, as does the cluster. I also have a vagcom and an OBD2 car scanner that get very weird values. It's not linear or otherwise believable. I've replaced the green top sensor and followed all the wiring back (looks good).

The fact that the rad fans turn on to high (10 seconds after you start the car in the morning) and the temp gauge shows overheating indicates to me that it's not the cluster that's messed---it's whatever is sending the overheat signal to the cluster and rad fan. It must be the same sender.

Does that make anything more clear?

I'm sorry for not describing it better, but I really hope to get some insight on this very tricky problem.

Thanks again in advance, I really appreciate it 

Danny


----------



## J Patterson (Apr 11, 2009)

*Wish I could help.. You have covered all I know.*

I would change the green top sensor again but unfortunately I suspect cluster.


----------



## CageyBee (Jun 15, 2000)

J Patterson said:


> I would change the green top sensor again but unfortunately I suspect cluster.


I'll change it again-it's not too expensive and easy to do. AND while I'm with you that the cluster is broke-what I have to know first (for peace of mind) is why the high speed fans come on too. Can the cluster trigger the fan to come on? 

Is the cluster merely a reporting device or does it allow for two way communication?

The dealer wants $1400 for the cluster... buh!


----------



## chosos (Apr 10, 2007)

if you're needing the cluster fixed, have you thought about emailing these guys to see if its a fix they can make before you spend $1200?


----------



## CageyBee (Jun 15, 2000)

chosos said:


> if you're needing the cluster fixed, have you thought about emailing these guys to see if its a fix they can make before you spend $1200?


Yes, I used the pixelfix people last year... I got the cluster "repaired" but by the time I got drove home the problem replicated itself 

I don't know what he did (replaced a chip in the cluster) but it was fine for a few minutes, tops. Waste of time and money unfortunately.


----------



## CageyBee (Jun 15, 2000)

chosos said:


> if you're needing the cluster fixed, have you thought about emailing these guys to see if its a fix they can make before you spend $1200?


BTW, what do they typically fix? Has anybody seen this rad fan problem being addressed by a cluster repair?


----------



## bauch1425 (Jun 29, 2006)

The cluster would not be causing your issue. Your green top temperature sensor has two readings - one which it sends to the cluster and another which sends to the ECU. The 49C reading on the AC unit is what is sent to the ECU. If 49C value matches the cluster reading (IE they're both high) then I'd think either you're really over heating a bit, or your temperature sender is bad. 

I've had WAY too many failed green top sensors. Believe I'm on my 4th or 5th. The black top lasted far longer than any of them.


----------



## CageyBee (Jun 15, 2000)

Finally fixed the problem. The connection at the back of the cluster was bad. The ground was intermittent.

Other symptoms (now that it's fixed, I realized some other indicators):
Fuel gauge and Temp gauge lighting was off. Sometimes they would flicker. Once the ground was fixed, this problem went away.

Also, the bad ground to the cluster caused the high speed fans to come on during startup. Contrary to this thread, the coolant fans *can be turned on by the cluster*, whether its by design or defect. It is in fact a possibility.

Thanks all for your help.

-danny


----------



## MiguelTTT (Oct 1, 2014)

Does anyone have any idea as how to fix the intermittent ground?


----------



## lite1979 (Sep 9, 2005)

Find out where the break in the circuit is, and fix it so it provides continuous current. If you're just jumping into this, I would recommend a Bentley repair manual so you can isolate the different circuits. It'll make discerning the different wires a lot easier.


----------



## Mcintry (May 23, 2020)

Sorry to resurrect a dead thread but cageybee how did you repair the bad ground at the back of your cluster I'm having a similar problem and would like to know b4 I tear the dash out


----------

