Coolant temp sensor

ZWBeamer

Member
Joined
Jun 27, 2019
Location
NC USA
TDI
2012 Jetta TDI
So my cooling fan will not shut off. Battery has to be disconnected or the fan will run it to death. Best guess I’ve been told is that it’s the coolant temp sensor. Can anyone please tell me where this is on a 2012 Jetta TDI because I have found so many different videos and such for different models or different years all in different locations and I can’t find it. Not as technically savvy as most on here so I don’t want to just start taking stuff apart to try to find it.
 

ZWBeamer

Member
Joined
Jun 27, 2019
Location
NC USA
TDI
2012 Jetta TDI
I found the sensor and changed it but it didn’t fix he problem. The fan is still running nonstop. Anyone know what the next step is?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
OBD works, that should have been the first step.

Fans can after run for up to 16 minutes. It is exceeding that? What does the Engine see as the coolant temp? What does the Climate see as the refrigerant pressure? Either of those can cause the fans to run. The fan module itself, integral with the left fan motor, can also cause this.
 
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ZWBeamer

Member
Joined
Jun 27, 2019
Location
NC USA
TDI
2012 Jetta TDI
It’s still running indefinitely. Tried letting it go for 30 minutes before disconnecting the battery. I have now ordered the radiator fan switch as well as the radiator fan control unit that I believe is actually inside the one fan? Those seemed like the next two logical steps to try to get this to stop running nonstop. I don’t know what the refrigerant pressure is. Could the refrigerant for the AC unit needing recharged have an effect on the cooling fan? It’s the cooling fan that’s running nonstop not the other fan that runs when the AC is on so I didn’t think about that
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Yeah, just ignore my advice and keep throwing parts at it. You'll get there... eventually. :rolleyes:
 

Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
You ordered a radiator fan switch for your car? Uh, sorry but I don't think you will find a place to accomodate that one in your car.

Also, what is the cooling fan and the AC fan? Shouldn't they ALWAYS work in tandem?

When CTS is faulty, the fan only keeps running for 1 minute or so.
If your fan is running non-stop, it means the fan (the one which has got the controller) is faulty - it's "brain" is damaged. Unfortunately, there is no fix for that because the controller is sealed.
Visit your local salvage yard and get a replacement fan inexpensively.

Before that, you may want to disconnect one of the red cables in front of the underhood fuse box (sorry but I don't remember which one, this information can be easily found online)
 
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ZWBeamer

Member
Joined
Jun 27, 2019
Location
NC USA
TDI
2012 Jetta TDI
@Henrick what I read was that one fan ran to cool the engine based on the coolant temp sensor and the other fan ran when the AC was running. Is that not correct? Also the radiator control unit and fan that I ordered are supposed to come as a set I believe. As far as the switch the diagrams that I have looked at had one listed so I was hoping it would be a cheaper fix than having to replace the whole fan unit but if there isn’t a switch then I was looking at the wrong diagram. Very possible. Thank you.

@oilhammer I am trying to follow your advice. Didn’t you say the fan module in the left fan could be the issue? That’s what I’m replacing. I had the shop check the OBD and the only code that he said came up was low voltage which I assumed was because the car battery had died from sitting for so long. I don’t understand what you mean by “What does the engine see as coolant temp? What does the Climate see as refrigerant pressure?” I don’t know what the engine is reading the coolant temp, there’s no engine temp gauge in my dash. I’m definitely not trying to ignore any advice I can get here.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
OBD (scan tool) gives you data, such as (but not limited to) coolant temp, refrigerant pressure, etc. Either of those items *could* be sending a false signal to the fan controller. Some cars even have an under hood temp sensor.

Normally those *should* be overridden by the 16 minute maximum time out, but I am not sure they would.

Generic scan tools are largely useless. You need something that speaks fluent Volkswagen, and can communicate with ALL the car's modules.
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
ZWBeamer
If you are going to do repairs on your own you really need a scanner to get the correct codes and other readings to diagnose it.
Generic code re-setters have been known to return the wrong data.

VCDS is the most cost effective way for this.
If you have a laptop VCDS Lite is a free download and can be used indefinitely.
You would need to buy an OBD cable or blue tooth adapter that works with it.

Check it out:
https://www.ross-tech.com/vag-com/
 

ZWBeamer

Member
Joined
Jun 27, 2019
Location
NC USA
TDI
2012 Jetta TDI
Thanks. I’ll look at figuring out what I’ll use. I use an ancient little tablet laptop and a desktop so I’ll probably just see what the best deal is on a self contained OBD unit. Oilhammer do you suggest any specifically?
 

Cedmx

New member
Joined
Jan 23, 2022
Location
Mtl
TDI
2013 vw golf tfi
Thanks. I’ll look at figuring out what I’ll use. I use an ancient little tablet laptop and a desktop so I’ll probably just see what the best deal is on a self contained OBD unit. Oilhammer do you suggest any specifically?
I know its a old thread but i have the same issues did you figure out what was the issue
 
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