'02 A4, 1.8T: replaced temp sensor @ firewall top of engine, temp guage is still not right. Usually stays at C...sometime after driving 10 + min will move to 1/4 - 1/2. It use to read middle all the time. Heater does not blow as hot as it used to and takes longer than normal. I noticed that the auxillary fans run when I start the car at cold temp...what do I look to check next? What sensor controls the fans? I own the Bentley manual but cannot troubleshoot...

thanks...

 

Any solutions to this?

My radiator fan runs at start up, preventing the coolant from heating up.

The fan DOES turn off when I switch off the engine...

 

I am not sure you realize that this post is from over 3 years ago.

Do you have a check engine light on your car?

 

possible fan issue here too on my 01 TT 225 Q, i have yet to see either engine fan run, its hit lo 70's here in pa, i can hear my after run turbo coolant pump run but engine fans have yet to run since purchase in dec 2011, heat guage starts about 1/4 and goes to about 5/8, i did replace faulty coolant sensor with green top have vag com, but not the best user, info to test fans with it would be appreciated. thanks in advance

 

Yes, I realize it's an old thread, but posters of this thread did not mention any solutions. I'm hoping that some of them found the solution, but just haven't yet posted them.

I do not have a check engine light on.

 

You start with the coolant temp sensor, make sure you don't have a coolant leak. bleed all air out of the system. make sure you have hot coolant going in and out of heater core. (feel the hoses next to battery)
for the radiator fans..... turn off the climate control head and see if the fan turns off.

the second "radiator" fan is actually the condensor fan. and turns on when the a/c is running. Because Audi uses variable output compressors the a/c is actually always on whenever the car is running. Just runs at virtually no output when the climate control setting are off. But no fans should operate when the climate control head is off.

kind of have to take away the obvious before getting into something crazy

 

Thanks AudiTek! I have addressed all of the things you spoke of. It's not the condenser fan. It's not a clogged heater core.

Does the ECT sensor send a signal to the radiator fan telling it to turn on?

I forgot to mention that my car takes long to reach operating temperature. The temp even goes down when I'm going downhill. I fear that my thermostat is stuck open.

When a thermostat is stuck open, does it send a signal to keep the fan running? Or, does the ECT sensor tell the thermostat to stay open and turn the fans on? (please tell me it's the latter)

 

Im having similar problems with my car. 2003 A4 B6 2.0 CVT sedan.
The temp gauge does not normally go up off its resting point.
The heater blows cold and only warms up a tiny bit with some driving.
The aircon works.
Im not relying on the heater to give me much indication of things since i found out about the decaying polyurethane foam problems in my A4B5's heater flaps. ( Even with this car, different warmths of air come out of different vents, otherwise i think the flaps are good as i have seen none of the foam fragments come out of the vents. I dont know if this cars heater systems the same as the A4 B5.)
Theres no 'Check Engine Light' on the dashboard
The radiator fans, both of them, start up about 20 seconds after i start the car.
If the climate control system is Off when i start the car the fans do not start up after starting the car.
IF the climate control is switched off, the temp gauge rises a bit, how much depends on how cold it is.
if its under 20°C, not much at all. Over 20°C, might get to 75°C. If its sitting idling, it once got up to 90°C.

i replaced the Coolant Temp Sender # 059919501A thats behind the head. ( Which is ridiculously easy to do in a NonTurbo NA version. If you do it with a cold engine ( like dead cold) you dont even have to do anything with the coolant. When the Sensor is out it coolant wont spill out since the systems under partial vacuum. DON'T undo the resiviour car beforehand or you loose the vacuum in the system.
i actually had to pump the radiator hose a bit to get the coolant level in the CTS receptable to rise so i could fit the CTS in.)
But that didnt change anything at all....

i find out that the thermostat is actually operated by a tiny heater inside the Thermostat housing, not by the water temperature. The heaters controlled by the computer, which in turns controlled by the CTS and computer programming. So i expect the outside temp sensor as well as engine management & maybe the fan switch thats down the bottom of the radiator on the left hand side where the hose comes out.
Next thing im going to check is that switch. I wish i could check the thermostat heater but i dont have a OBDii reader that works. Or a wiring diagram.
After that, i expect its the thermostat in the housing # 06B121111G . The last letter changes depending on the updated version.
I'm​​​​ not buying a Chinese version, prefer a SWAG or Mahle & i hope the Crankcase ventilation hose # 06B103211H that i have already ordered turns up before the thermostat so i can replace both at the same time. The alternators got to come out to get in there to replace these parts.

 

I took the underbody stone guard off today & checked the fan switch, its 'open' so no power will go thru it. I expect its a NO switch.
I found the spigot mounts polyurethane foam bumper has fallen apart so i need a new one of them. Its a heap & easy job to fix it.
Theres also missing stone guard screws & i found 10 screws & backing for less than $5 on the internet.
The thermostat parts being ordered today, about 6 days away but only a thread post away for yous guys, lol.
Its $85
Also the 2 lower front arms that the shock absorber attaches to have splits in the rubber, so they need replacing soonish.

 

My radiator fan runs at start up, preventing the coolant from heating up.