No voltage to cabin temperature sensor 1K0907543E

Dec 15, 2022
11
1
New poster here. Seat Leon ST MK3 2014 1.4 138hp petrol
I have searched the forums but couldn't find this particular combination. Please post a link if I have missed something.
I have the common fault with the climate in my car. From the beginning the interior wasn't warming up until a long way in to my journey. I started to investigate. The header tank was a little low, so I topped that up and let it run with the heater on high but that made no difference. I then noticed that the passenger side vents were blowing hot air but the drivers side vents were blowing cold air. I searched the forums for this, to find out that it's probably the climate temperature sensor in the drivers side vent. I have removed this, popped it on a multimeter, put it over a kettle and the meter changes, which leads me to think it is functioning. I then took the meter to the car to check that I have 5 volts at the leads that supply the sensor. Try as I might, ignition on or off, I couldn't get a voltage reading from the wires.
I think this is my problem, no voltage to the sensor, but where do I go from here? A single sensor won't have a fuse and the wires disappear of into the loom and I'm not messing with that without expert guidance!
Please help as it's minus 6 outside and the driver's side of my car thinks it 30+, so is pumping even colder air in to the cabin!
Thank you in advance
Andy
 

RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
Have you checked for a voltage on the temp sensor on the passenger side, just to be sure that what you are seeing is actually what is there?

Typically, it is the flap motors that cause most of the problems with heating/cooling, in your case the driver's side temperature flap motor.

Edit:- is the multimeter that you are using got a high enough terminal impedance, ie it is not pulling the low current supply down?
 
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mty12345

Active Member
Jun 17, 2011
3,727
450
bristol
I agree with the above, very good advice. It's quite possible that there is no 5 volt reference for that kind of sensor, the ECU may just be measuring the resistance which with changes with temp. As RUM4MO said, I'd definitely check the passenger side before you go chasing your tail
 
Dec 15, 2022
11
1
Thank you. I do have an update, if you could help. I checked the voltage at home with my meter and there is 5volts at the wires! Testing the sensor over the kettle there seems to be plenty of resistance movement from cold to hot, so I don’t think it is the sensor.
Where do I need to look next please?
Thank you
 
Dec 15, 2022
11
1
I’ve just sat in the car turning the driver side temperature gauge from Hi to Lo to Hi repeatedly and I now have warm air coming out of the vent (not as hot as the passenger side but no longer icy cold).
An advice gratefully received.
 

RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
Sounds a lot like the driver's side temperature flap motor positional feedback potentiometer is dirty/failing, that is what normally happens, demanding Hi > Lo, Lo>Hi repeatedly might make it work for longer and offer up hotter air, or maybe not, if so replacing that flap motor should solve your problem.

Remember that this is only logical guessing, if you had VCDS or similar you could change the demanded temperature and monitor the flap motor movement and by doing that work out if indeed it was a fault flap motor, plus if you performed basic setting, you would be able to see if the flap motor was free to move through its entire intended arc.
 
Dec 15, 2022
11
1
Update!
I took the car to get the diagnostic check as recommended. Central VW Audi in Erdington, Birmingham did this for a set fee of £49. Nothing untoward came up, so they very kindly did some further checks. They checked the temperatures of the pipes entering and leaving the heater matrix. Basically, hot going in and luke warm coming out, suggesting a blocked heater matrix. They quoted me £1178 inc vat to replace the heater matrix.
I decided I would attempt this repair myself. I purchased the matrix, some flush and plenty of G13 antifreeze for around £180 inc vat. I attempted the repair, outside, one recent rainy weekend. I managed to expose the heater matrix but it proved too difficult to get under the car to remove the tray and undo the bottom rad pipe. I decided to put it all back and look for another solution.
Through a friend of a friend I found a smaller, more local garage who quoted me a much more reasonable price as they knew the knack of sliding the matrix out from the side without removing the whole dash. They did it in a day and my heating is absolutely perfect.
The guy in the garage said that he is doing plenty of them now across various Seats, Audis, etc.
I'm not saying every time it blows hot one side and cold the other it's the heater matrix but in my case and several others it was!
Thank you everyone for your help!
 
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RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
Oh, good that you have sorted this out!

Normally, or typically, this blocking up of a heater matrix in a VW Group car was being blamed on the silicate pouches in the coolant reservoir breaking open and the "crystals" circulating around the coolant system and getting trapped where there is a small bore piping location - which the cabin heater matrix has!
So, does your coolant reservoir have "Mit Silicate" printed on its upper body? If so, has that reservoir been replaced with one that does not have this printed on it? G13 seems to have been a slightly unsuitable/unsatisfactory version of coolant additive in that with some engines where the coolant got very hot, the G13 lost some of its protection, and so VW Group needed to start fitting coolant reservoirs that had these silicate pouches which slowly dosed the coolant with extra silicate to replace what had been "taken out" of the coolant. Hopefully going forward, G12evo which is the only new coolant being sold by VW Group parts departments, has solved that problem and so the need to fit these silicate pouches to coolant reservoirs.

There was another suspicion that casting sand had been left in some of the engine castings, and with time, it was breaking free and again collecting in the heater matrix, but that seemed to be a TDI only issue.

Edit:- when I replaced the G12+/G12++ in my 2011 Audi S4, I refilled with G12evo 50/50. When I eventually take bits of my wife's 2015 VW Polo so that I can check/replace the HP fuel rail securing bolts - a known "issue" with any/all EA211 engines, I will replace the drained G13 coolant with G12evo as I've been checking the ph of this coolant over the past 6 years and it is heading towards being acidic a lot quicker than the G12+/G12++ was in my 2011 Audi S4 - that 2015 VW Polo 1.2TSI 110PS did not get fitted with a Silicate pouch at factory, so maybe that is why the ph is heading towards being acidic quicker than expected.
 
Last edited:
Dec 15, 2022
11
1
I had a quick look yesterday afternoon, as I was advised to check the coolant levels. I couldn't see anything on the expansion tank denoting Silicate.
As I used a smaller garage to get the work done at a reasonable rate, I am now starting to worry that they won't have used either G13 or G12 evo and probably just off the shelf antifreeze. Should I be concerned? It would usually go in for its annual service/MOT at the end of August, can I wait until then to get it changed?.
 
Dec 15, 2022
11
1
Hello, it is a red/orange colour.
I checked again on the reservoir and there is no mention of Silicate. The only thing printed on there is G13.
 

RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
Genuine VW Group coolant is red<>purple<pink>, I've never managed to develop the ability to distinguish between the 3 colours to be honest. So your car does not seem to now have VW Group approved coolant, but can you check what version/brand of coolant it is to make sure that it is okay to mix this with VW Group G13 - okay most if not all of the original G13 will have been flushed out, so maybe not an issue wrt to compatibility with original coolant.

So, I wonder where the debris came from that caused your cabin heater to get blocked - could this be just G13 degrading too quickly over time due to the lack of these Silicates pouches that VW Group found the need to fit to some cars with certain engines? If so, maybe more cars without Silicate pouches and original G13 will start finding their cabin heaters partially chocked soon!
 
Dec 15, 2022
11
1
Update. About 3 months ago my aircon stopped working. Seat main dealer were supposed to have done it August 2022. They checked, no leaks, topped up and was fine. The heating has been fine after having the matrix replaced in April. At the moment, I have intermittent or weak air-con and a mixture of hot and cold coming out of the vents when I have the heating on.
What should I do next?
 

RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
It could now be the temperature flap motor that is not controlling the air blending as it should. If you were able to connect a fully VAG compliant scan tool, like VCDS to the car and check the performance of the flap motors, you might be able to prove/dismiss idea.
 
Dec 15, 2022
11
1
It could now be the temperature flap motor that is not controlling the air blending as it should. If you were able to connect a fully VAG compliant scan tool, like VCDS to the car and check the performance of the flap motors, you might be able to prove/dismiss idea.
Can you recommend one to buy? Could you include a link to Amazon or EBay please?
 

SuperV8

Active Member
May 30, 2019
1,314
576
Update. About 3 months ago my aircon stopped working. Seat main dealer were supposed to have done it August 2022. They checked, no leaks, topped up and was fine. The heating has been fine after having the matrix replaced in April. At the moment, I have intermittent or weak air-con and a mixture of hot and cold coming out of the vents when I have the heating on.
What should I do next?
Car aircon systems do leak slowly over time, there are not perfectly sealed like a fridge system - there is an 'acceptable' leakage allowance % vs years. If this is your first aircon refrigerant top-up on your 2014 car this would not concern me, if you were having to do it every year of two then that would.

Flap motors behind your dash control your heat/cold/air distribution. These can get stiff from lack of use, and even brake the linkage. Good practice to cycle your hot/cold/windscreen/feet controls to cycle the flaps every now and then. I noticed on my previous Audi on a journey, one side was hot, and the other was cold - but 'playing' with the controls got it working again.
There is a flap motor re-calibration you can perform on the Leon without any diagnostic interface - have a search on here.
 
Dec 15, 2022
11
1
Hello All
After trying to reset the flaps by pressing the A/C and front vent a/c button together (lots of times) and then moving on the doing cycles of hot then cold and then forcing air from screen to front to feet, nothing is making a difference.
When the setting is on HI temperature, I get hot air from both passenger vents but cold air from both drivers side vents.
My preference would be to fix this by changing the flaps/motors but looking at some of the diagrams, I think it will be too much for me (lack of expertise and tools) and that a garage would want a lot of money as they will invariably want to take the dash out.
I like the car, I've looked after it, it's done 95K, full SEAT service history , etc.
I'm worried that if I part exchange it, I'll get something with more problems - the age old dilemma.
Is there an easy fix for this? Can I get a cheap VCDS reader to see what's actually going on and if so, where? My final ask for help! Much appreciated.
(Seat Leon FR ST MK3 2014 1.4 138hp petrol) Andy
 

Walone

Active Member
Feb 10, 2016
1,533
418
Near Heathrow
Hello All
After trying to reset the flaps by pressing the A/C and front vent a/c button together (lots of times) and then moving on the doing cycles of hot then cold and then forcing air from screen to front to feet, nothing is making a difference.
When the setting is on HI temperature, I get hot air from both passenger vents but cold air from both drivers side vents.
My preference would be to fix this by changing the flaps/motors but looking at some of the diagrams, I think it will be too much for me (lack of expertise and tools) and that a garage would want a lot of money as they will invariably want to take the dash out.
I like the car, I've looked after it, it's done 95K, full SEAT service history , etc.
I'm worried that if I part exchange it, I'll get something with more problems - the age old dilemma.
Is there an easy fix for this? Can I get a cheap VCDS reader to see what's actually going on and if so, where? My final ask for help! Much appreciated.
(Seat Leon FR ST MK3 2014 1.4 138hp petrol) Andy
Where are you located? Someone on here may be willing to help.
 
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