# Coolant Temp Sensor Wiring help



## Benwaa (Feb 22, 2017)

Hope fully someone will be able to help with this. Car is a 2001 BAM 225 coupe
I've a code i keep getting that's 01039 for the coolant temp sensor (G2) open or short to ground. 
The issue it causes is to register the coolant temp at 121 degrees C, when in fact it's at normal temp of approx 92 on a thermometer in the header tank to really check.
I've changed the sensor three times, and also swapped it over with a mates who we knows is working and tested the last one with a multi-meter too as per a video i found on how to do that. it's not the sensor, which leaves only the wiring.
So a visual inspection of the plug reveals nothing obvious going on, and following the wiring back to where it joins the other sensor wires and is heat shrink-ed together, there's also nothing obvious (i now that's not a 100% guarantee though).
Now this is where it gets a bit sketchy for my skills as electric stuff isn't the strong point at all.
I have the following measurements on the plug connector, if someone could help make sense of what's what and why and which wire would be best to look at/follow etc would be great.

Tested with ith the ignition on and engine not running:

Pin socket 1 (purple wire)
6.28v (no resistance measured)

Pin socket 2 (Brown/White)
is grounding and with a resistance of 1.5 ohms

Pin socket 3 (Green/Blue)
4.63v (no resistance measured)

Pin socket 4 (Brown/Blue)
is grounding with a resistance of 0.009 ohms

Which wires should i be looking at? i know one pair should be for the G2 and the other for the G62 but i don't know which and i'm not sure of which wire would be causing the short to ground either obviously. I don't have a wiring diagram and the only one i can find for the same coolant sensor isn't for the TT and is for a TDi A4 so don't want to take the risk of things being opposite or whatever on the TT. And i suspect that the voltage should really be the same for both pin 1 and pin 4

thanks in advance for any help at all


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## Hoggy (May 8, 2002)

Hi, I'm thinking about it. 
Does the gauge indicate high temp even with sender plug disconnected?
High resistance means low temp on gauge.
I'm still thinking.
Hoggy.


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## Benwaa (Feb 22, 2017)

Hi Hoggy!
No it doesn't.
I'll add some more info now I've also thought more about it.
I went for a drive on Monday, the temp sensor played up as usual showing high temp both on dash and 49c.
After maybe 30/40mins of driving the temp gauge started to show the correct reading as did 49c.
It was then fine the rest of the drive. I didn't go out in the car again that day though.
Next day I went to start her up and did my obsessive thing of checking 49c and noticed the temp sensor was showing 42 degrees, this had reached 86 by the time of driven maybe quarter of a mile. 
Stopped at a mates and then followed him the 18 miles to the scrap yard, on the way back the temp reading dropped on 49c to -10 briefly before hitting 121 again.
About 4 miles from home the reading returned to what should be correct 90ish.
I've not been for a long enough drive to recreate this issue. It's just showing immediate high temp (well it counts up almost second by second 1 degree by 1 on the 49c) 
It has been getting progressively worse though since beginning of August


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## desertstorm (Apr 25, 2017)

Hi, Just made a copy of the wiring diagram for the engine wiring on a 2001 BAM. Unfortunately it's a 3.6Mb file so can't append it directly to this post. I have uploaded it to my dropbox. You can download it from this link.

https://www.dropbox.com/s/tw9lvjdr7gub7 ... g.pdf?dl=0

Temp sensor wiring is on page 9. The G2 sensor is the one connected to the instrument cluster. G62 connects to the ECU. If you were to use VCDS and log engine temp from the ECU you would be seeing the G62 sensor output and I am pretty sure it would read correctly.
I think it's a reasonably common issue that the temp reads incorrectly on the cluster due to a fault in the cluster itself.
You can see the G2 sensor connects into the cluster itself on page 13 on track 149.
Make sure the brown / white earth on pin 2 is 100% good. You have got a very low reading for the earth on the G62 sensor. The G2 earth at 1.5 ohms seems a little high.

Karl.


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## Hoggy (May 8, 2002)

Hi, I remember Wak had a false high temp prob which also affected the Code 49 reading & that was caused by a faulty dashpod. May be worth contacting Wak if he doesn't see this post.
Hoggy.


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## Benwaa (Feb 22, 2017)

Thanks Karl, just saved that to my Dropbox too. Really appreciated 

So he wire I should check firstly is the brown/white one (pin 2) you say? Will get on that then.
What *should* the resistance and voltage be at each pin socket? Anyone know?

Not too sure about the cluster issue as it's been repaired last year, and 49c shows the same temp. Did a vcds test of the cluster yesterday funnily enough (just playing around learning what I can do with the prog after scanning the codes again) and it passed without issue too apparently.

Fault is intermittent anyway but getting worse so something is obviously degrading somewhere


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## desertstorm (Apr 25, 2017)

Not sure what the voltages should be on the pins that goto the ECU and the cluster. They are the inputs to the measuring cct that determines the value of the resistance of the thermistor. The G2 and G62 sensors should be earthed at one end. Recheck the value of the resistance to gnd on pin 2. That should be very low.
The cluster is converting the value of the resistor into a temperature value and displaying it on the gauge. It also digitally encodes it and sends it via the CAN network so other modules can use that information. Thats why you see the value in the AC unit under 49C as being the same.
https://www.linkedin.com/pulse/automoti ... l-mucevski

You could try reseating the connector on the back of the cluster that provides the connection to the G2 sensor.


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## Benwaa (Feb 22, 2017)

desertstorm said:


> Not sure what the voltages should be on the pins that goto the ECU and the cluster. They are the inputs to the measuring cct that determines the value of the resistance of the thermistor. The G2 and G62 sensors should be earthed at one end. Recheck the value of the resistance to gnd on pin 2. That should be very low.
> The cluster is converting the value of the resistor into a temperature value and displaying it on the gauge. It also digitally encodes it and sends it via the CAN network so other modules can use that information. Thats why you see the value in the AC unit under 49C as being the same.
> https://www.linkedin.com/pulse/automoti ... l-mucevski
> 
> You could try reseating the connector on the back of the cluster that provides the connection to the G2 sensor.


Ok cool, so pull out the dashpod and check all the connections with its plug and socket are seated right you mean? I'm happy to pull that out and chek it's plug/socket but not pull it apart in any way


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## silkman (Jul 29, 2004)

Following this as by the looks of it I have something very similar.


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## Wak (May 6, 2002)

My issue was as described above in addition to high temps and 49c matching and trying 2 new sensors with the high temps the fans were running at high speed.

I took the punt on a replacement dashpod and that cured it .


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## Benwaa (Feb 22, 2017)

Thanks for all the info guys, realy appreciated. 
So armed with all this info and wiring diagram, i'll start with checking the wires to the dashpod this weekend (wak informed me he wasn't getting the code as i do, but that can mean nothing too i guess) and if all looks ok and tests out ok with the multimeter etc then new dashpod seems to be the way forward.
So with that (scarily) in mind, whats a) the cost form audio for one sorting out? or b) a second hand one, but what's the cost of getting the thing coded to the ecu and the immo keys to it etc? will audi do this on a second hand unit i fitted? any ideas on this would be helpful.

Also, going down the second hand route, how would one go about getting the skc/pin from the second hand dashpod to be able to recode myself using vcds? i know i can get it from my current one with a bit of software i forget the name of, but unsure if that'd also help with the donor one. 
If it comes to that too, anyone know of anywhere that would re-correct the mileage to what it should be on a replacement pod?


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## Benwaa (Feb 22, 2017)

Some extra info to add:

VCDS shows the temp following what I see on dash and 49c, doing a live log quickly for a couple of minutes on the first start up of that day shows it rising immediately but the graph does show some drops that are huge to what looks like proper temp.
Oil temp on ac 51c showed it at maximum 90 degrees almost immediately too, however having turned it off and back on again that's now registering a more acceptably accurate figure whislt the coolant temp still is borked

The warm up auto choke uncle is working correctly though, so ECU must defo be getting the correct temp from the g62 side ok


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## Hoggy (May 8, 2002)

Hi, Code 51 always settles at 90 regardless.so best ignored.It's not actually oil temp anyway.
Hoggy.


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## Benwaa (Feb 22, 2017)

Mine always slowly counts up to that over a couple of miles. But yeah you're right hoggy  it doesn't ever go over 90. Was just strange it showed 90 immediately today whereas whenever else I've lookef at that on first start up it's been around whatever the general ambient temp is.


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## Hoggy (May 8, 2002)

Hi, I can't prove it but my thoughts are Code 51 is the coolant temp to ECU.
On some Code lists it's shown as Engine temp.
Hoggy.


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## Benwaa (Feb 22, 2017)

Hoggy said:


> Hi, I can't prove it but my thoughts are Code 51 is the coolant temp to ECU.
> On some Code lists it's shown as Engine temp.
> Hoggy.


haa yeah that'd make total sense actually! thanks hoggy again 

So i have a further update, i pulledthe daspod out, well a bit out without deisconnecting the plugs into it, i gave the wires round the back a bit of a wiggle and the gauge moved to the middle where it should! i gave them a wiggle again and BEEP! temp maxed out, another wiggle closer to the pod and again temp down to approx same area as engine temp showing in vcds!
Another tiny wiggle this time of the purple plug into the left side of the pod (left side is me facing the proper front of the pod) and again movement of the gauge! 
Pushed the pod back into place and so far it's been fine. evidently some issue with the wiring to the plug then, i suspect at this stage that maybe due to the pod previously being taken out to be sent to bbereman by the previous owner they weren't exactly too careful in getting it out (one of the white tabs is missing as potential evidence) and may have done some kind of damage to the wiring into the plug or the plug itself. 
I'll soon find out over the weekend if this is that case, as i haven't had a single day in the passed couple of weeks where the car has had it's first start of the day and the temp reading is borked. tomorrow *should* hopefully be back to normal.

Will update further if this is the actual solution or not as things progress. Will keep this thread updated with everything i do until the solution is found in the hope it may help others.

Got to say a massive thanks to you all so far! you've all helped out amazingly and i certainly wouldn't have been at the dashpod already without all your help. so again, thanks!


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## desertstorm (Apr 25, 2017)

Glad you are getting somewhere with it, could be a poor connection on the harness to cluster or possible a dry joint on the PCB in the cluster that you are disturbing. Either way your more in the area where the issue is.
The connection to the temperature sensor is on the T32 connector pin 8. Thats the blue connector. 
You can see the pin designations in the connector if you look at the end of it very closely the pin numbers are marked.


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## Benwaa (Feb 22, 2017)

desertstorm said:


> Glad you are getting somewhere with it, could be a poor connection on the harness to cluster or possible a dry joint on the PCB in the cluster that you are disturbing. Either way your more in the area where the issue is.
> The connection to the temperature sensor is on the T32 connector pin 8. Thats the blue connector.
> You can see the pin designations in the connector if you look at the end of it very closely the pin numbers are marked.


Ah awesome! thanks for that info, handy to know to cut the time faffing about down so really appreciated 
Left the car for a few hours this evening since probaly half 6 until about 20 minutes ago so 5 hours - enough to cool down a fair bit.
The temp showed OK before starting but went maybe a little too high too quickly when i started it up, going up to 109/110 degrees, as it's dark and wet out i just tried to wiggle the dashpod by holding it finger and thumb by the recesses for the gauges, it barely moved at all (1mm maybe?) but the temp gauge dropped back to what i would assume is pretty much the correct temp immediately. 
so whichever it is, the connector possibly, or as you say a dry solder, it's very isolated to the dashpod end of things as whilst i would say the movement i got could have maybe slightly adjusted the seating of T32 connector or how the dashpod is attached to it's relevant pins. 
I guess it's a possibility then that on the longer runs it starting to suddenly work would be maybe randomly resented properly as the car had nicely warmed up with the heating on a bit would cause tiny bit of expansion, and a bit of vibration form driving too. And this is why in the mornings when it's properly cold from the ight etc it's contracted a little somewhere and that dodgy connection has moved just enough again. And the more it's happened the worse the issue is obviously going to get. I hope it's the wire or connection in the in the connection haha
At least i also know now that if the gauge goes out again i can temporarily fix it with a grab n a wiggle


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## Benwaa (Feb 22, 2017)

Bit of an update, pulled the daspod out, tested and inspected all the wiring and all ok there. On further inspection and a bit of gentle wiggling it appears the problem is with the pins on the back of the pod and how they're attached to the pcb behind.
Called up bbareman to find out about the status of the warranty on it as it's only the beginning of last October they fixed it for the previous owner.
The really crappy thing is the warranty stays with the customer not the vehicle. So as I wasn't the original customer with them the warranty is void. Rather crappy way to be that imo, especially after only year since "repair".

On a plus note (if you can call it that) had a good convo with the guy and managed to get advice to go through eBay and use the make an offer bit, they'll accept £110 all in for the repair. Whilst I shouldn't have to do that imo and only pay for carriage, I don't have any other option really.

So as it's half term next week and I'm stuck in work this week, looks like I'll have to get this sorted in a couple of weeks and just put up with the constant high temp warning on the dash


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## arash_pyk (Apr 12, 2020)

Hello all, I know the thread is 3 years old but I as wondering if a solution was found to the problem?
(March 02 225 BAM engine)

I have a similar issue with the following symptoms:

-I have a cold start problem for a year (intermittent issue [smiley=bigcry.gif] ) where the rev counter does not fluctuate while the engine is being cranked, at the same time 49C reads -10. The problem normally disappears if I turn the ignition on and off a few times and press the throttle while cranking. as soon as the rev counter starts to move the engine starts and the temp in 49C slowly ramps up from -10c to 30c..., If I turn the engine off and on immediately after this issue happens it starts fine on one crank every time but the 49C can still show a wrong value?!!

-Once engine is warm the temp is anywhere from 88c to 100c and car runs fine. car also idles properly after cold start or warm start.

-rev counter always work fine while the car is running

-I always have a G2 short to ground or open fault even after changing the sensor.

-sometimes a repeated relay clicking sounds comes from behind the fuse box while cranking the engine with rev counter not moving. but only sometimes.

-fuel consumption has gone up from 26-28MPG to 19-22MPG for economy city driving

####Things that I have investigated and rectified:

1)Once I had a G28 fault (around 6 month ago) I changed the sensor and it never came back again!

2)Had a warm start issue that was indeed G2/G62 issue. I had a fault on both G62 and G2. it had a cheap eBay one fitted I replaced it with an OEM green one for 27GBP but I still get a G2 fault on VAGCOM

3)MAF/MAP/CAM/Crank sensor were all either changed or cleaned and seem to work properly

4)cleaned all earth points I found (on the battery/ to the right of battery / next to coil on the engine / gearbox /behind fuse box /cleaned connectors to the ECU with contact cleaner as well but nothing looked rusty so it was unneccessary)

5)Looking at the wiring diagram, the only thing that G62/G2 shares with G28 speed sensor (i guess this is the rev counter sender?) is connection "220 earth connection (senser earth) - in engine wiring harness". Given that both Temp sensor and engine speed sensor are being intermittent as once I guess this is my issue. Can anyone point me out to where this wire ends up? and what do the mean by engine wiring harness?

6)dash pod had been replaced previously by Audi. but since I had it, the temp guage was faulty and was not returning to below 50c when ignition was switched off. (49C was showing the correct temp though) LCD also had lines and a few of the LEDS were flickering. I repaired all of these issue myself. Found several cracked solder joints especially on larger SMD components. I reflowed/resoldered as many pads as I could, changed the LCD and Temp gauge motor, recalibrated using VAGCOM now all dash problems are fixed.

7) while fixing the dash pod I did the following continuity tests:
-Pin 7 and 9 on blue connector on the dash are indeed connected together with 0.2 ohm. that is load ground and sender 
ground.
-If i measure resistance between pin 2 and 4 on temp sensor with blue dash connector disconnected from the dash pod, 
the resistance is high, as expected
-Now if i connect the blue connector to the pod the resistance between pin 2 and pin 4 of the Temp sensor is 0.6 ohms 
which is also normal but. the resistance between pin 2 to battery ground is around 5 ohms (i think its too much unless the 
dashpod does not like resistance measurement while is powered up?!).
- There is good continuity between dashpod ground to temp send ground. and good continuity between G2 signal (149 in 
wiring page 9 and pin 8 on blue connector) to dashpod

I am tempted to short pin 4 and 2 on temp sensor but I am scared of creating a large ground loop around the engine bay. I guess there was a good reason for separating the 220 ECU ground and 269 dash sender ground

my other option is to connect pin 4 of G62 temp sensor (connection 220) to a chassis ground and hope G28 will get a good ground form there too but I am scared of frying the ECU.

is there a ground point in the engine bay and elsewhere that i missed and need to clean? I am guessing a wire or a connection is degrading somewhere, the issue is not dependent by the environment by the way it happens in dry or humid, hot or frosty days...

P.S. it is my first forum post sorry it is too long.
Hoggy thanks for your swift and concise replies on TT forums, I have managed to fix many of my TT issues over the years by your posts.


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## Hoggy (May 8, 2002)

Hi arash_pyk, If you turn Ign On & leave for a couple of minutes before attempting a start, does the problem still occur?
I'm thinking it may be a dash pod prob & the delay may allow enough time for the processors to warm up.
Hoggy.


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## arash_pyk (Apr 12, 2020)

Hi Hoggy,

Thanks for the quick reply, I have never tried that. I will next time it happens and post an update here. 
I did recently repaired the dash and resolders all IC pins and the issue hasn't happened yet but that doesn't mean that the dash is not faulty still. The problem is intermittent which makes it extra difficult to troubleshoot.

P.S. I noticed there is actually a heater element under the screen of the dash, I thought that was very neat.

Thanks again Hoggy


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## Hoggy (May 8, 2002)

Hi, I don't believe the false coolant temp indication is causing the startup problem but faulty dash pods have been known to cause Code 49 to give false indications.
I'm thinking a faulty dashpod may also be causing the intermittent crankshaft speed/failing to start prob.
The dashpod is so involved in many things.
Hoggy.


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## arash_pyk (Apr 12, 2020)

Quick update!

My old start issue has come back again with a new problem.

1) coolant gauge on the dash pod and on 49C reads either -10C or 121C and nothing in between but prior to re-soldering parts of the dash pod it used to read -10c sometimes and never 121C. It would read the correct value most times.

2) once again I have the original issue of the cold start when gauge reads -10 and rev counter doesn't move on the cold start.

3)possibly a related problem: windscreen washer pump does not make a sound nor spray but headlight washers work - more importantly the dashpod throws low washer fluid warning on the screen every now and then but not always despite the tank being full. not sure of this one is also a dash related issue combined with a faulty pump. or just a faulty fluid level sensor and pump.

- Hoggy I took your advice on leaving the ignition on for couple of minutes and it seemed to work but hard to tell. Do you think I should send the dash pod off for a rebuild. If so any suggestion for a good place in the UK?

Thanks


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## Hoggy (May 8, 2002)

Hi Arash_pyk, Is the battery at full volts or does it struggle to spin over.
Headlight washers use a seperate pump so investigate that & the washer fluid level sensor.

Dashpod repairers.
https://totaltronics.com/instrument-clu ... placement/
https://cartronix.co.uk/product/audi-lc ... eedometer/
http://www.bba-reman.com/gb/content/das ... ster_range
http://www.clusterrepairsuk.co.uk/
http://www.ecutesting.com/catalogue/pro ... 20980.html

Hoggy.


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## Mcintry (May 23, 2020)

Sorry to revive a dead post but what did the OP do to resolve his issue. I am having a similar issue saying g2 grounded but my temp gauge is at zero and my climate control stays at 120


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## Hoggy (May 8, 2002)

Mcintry said:


> Sorry to revive a dead post but what did the OP do to resolve his issue. I am having a similar issue saying g2 grounded but my temp gauge is at zero and my climate control stays at 120


Hi, Check the plug/socket/cables for the coolant temp sensor, if all looks O.K. replace the coolant temp sensor & use OEM part No 059919501A for the oval sensor & 078919501B for the square sensor, not an OEM quality from Ebay etc.
But of course it could be a faulty dashpod causing the prob.
Hoggy.


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## arash_pyk (Apr 12, 2020)

Hello I am back again with my cold start problem just watched a video on false overheating which inspired me to try to fix the issue again. here is the link to the video that I found in some TT MK1 false overheating forum.

https://www.youtube.com/watch?v=c2hofPi ... e=emb_logo

I am copying what I commented on the video which also recaps the issues I was having. any help would be appreciated. i really want to get to the bottom of this problem.

I have an intermittent cold start issue where coolant temp on 49C shows -10 then shoots up to 121 within a few seconds, restarting the engine fixes the issue. Interesting thing is that when the engine does not start (when cold never when is up to temp) the rev counter also does not move while the starter motor is cranking the engine. I check the wiring diagram and it appears both G2 coolant sender and rev counter share the same sensor ground. This makes me think I have a loose ground connection somewhere (in the wiring document it says ground connection in engine wiring harness??!! where the hell is that?) I have checked the wire from coolant to the back of dash pod and the resistance was low can not remember the exact value but just less than 1 ohm (which is still a bit high imo)

I reflowed the entire dash pod once (i am an electronic circuit designer btw) and changed the coolant sensors many times .

One of the coolant sensor pair (cannot remember either G2 or G62) always shows a short to ground fault on VAGCOM even when a new one is put in place. the other one when it worked showed 90ish degree both on 49C and dashpod. when I reflowed the dash pod, the problem appeared to be fixed for a few weeks then came back. first the needle went back to the old issue of resting at 60ish deg when the engine is off like it used to prior ro reflowing. Then the 49C temp became binary meaning it either shows -10 deg or 121 deg (mostly -10C) whereas before reflowing it would more often have cold start issues (shows -10C at 49C and rev counter not moving when cranking the engine) when finally the engine started the 49C slowly would rise to the actual value around 88C-92C???? any idea. Also since the issue came back 49C never shows the correct temp again it is only on -10C mostly and sometimes on 121C while 51C shows 90 when engine is warm.

I have had this problem for two years and it annoys me so much. Not being able to troubleshoot is really damaging my ego given that I know its an electrical issue and I am an electronic engineer with expertise in sensor design :roll:

Also in the recent cold weather the cold start problem has not been as bad. when the engine starts, the only issue is 49C shows -10 while the needle sits at 60is. after afew seconds that the engine is on, the coolant temps it shoots to max (121C) and dash overheating alert, needle on red zone etc... I can make it go away by turning the engine off and immediately back on. 
This is driving me insane [smiley=bomb.gif] [smiley=bomb.gif] [smiley=bomb.gif]


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## silkman (Jul 29, 2004)

Pic saved from another thread; when you have a -10 or +121 Temp condition can you try pressing hard on the dashpod on the square areas in the picture to see if it corrects itself?


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## Lex885uk (Dec 6, 2021)

arash_pyk said:


> Hello I am back again with my cold start problem just watched a video on false overheating which inspired me to try to fix the issue again. here is the link to the video that I found in some TT MK1 false overheating forum.
> 
> https://www.youtube.com/watch?v=c2hofPi ... e=emb_logo
> 
> ...


Good evening Arash! I know this is an old tread, but anybody was able to fix this issue? I have exactly the same issue on my 225 TT. Very annoying. My dashpod temp gauge is not moving at all most of the time and the 49C shows -10. But intermittently when I cold start the car the daspod gauge is jumps to max and the fan kicks in full speed like the engine is overheated. If I turn off the car and back on its working ok but -10 again.

I have replaced the coolant temperature sensor already. My cluster probably has been fixed before as it is a 2002 TT and the LCD is mint no dead pixels or lines at all. Also the Fuel level guage also acting funny sometimes, but it still reads, but do not think the correct reading.

If anyone solved it please share!


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