# CEL on, code P2181 ("Cooling system performance") diagnosis



## dtgriscom (Feb 14, 2007)

I have an '03 Golf GL, and my Check Engine light has been on for a while. I finally picked up an Actron CP9180 AutoScanner, and read the code: P2181, which is described as "Cooling system performance". From what I can tell, though, everything is working fine:
- Both radiator fans turn on and seem to run fine (it's cold, so I had to turn on the AC, which meant I had to wait until it was at least 40F out)
- The dashboard temperature gauge warms up to 190F and locks there (yes, I know it's designed to lie, but it's at least doing what it's designed to do)
- The coolant temperatures read by the Actron go up to about 174 when the dashboard hits 190, and then stay between 175 and 205
- Although I'm not certain, I think I've found the engine temperature sensor, and it's green (which is reputed to be "good").
I tried clearing the engine code, but a few days later it came back (while driving on the highway). I've gotta get this inspected, so I need to solve it.
I don't think it's the temperature sensor(s), since both the dash and engine computer temperatures seem to be working. I don't think it's the fans (unless there's an issue with the fan speed being wrong). I don't think it's the thermostat, since the coolant temperature seems reasonable. I don't think it's the water pump, since again the coolant temperature seems reasonable. Add all this together, and the problem doesn't exist... but it does...
Any ideas? Anything else I can look into before I hand it to the dealer (which would be a royal pain in the wazoo)?

Thanks,
Dan


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## ps2375 (Aug 13, 2003)

*Re: CEL on, code P2181 ("Cooling system performance") diagnosis (dtgriscom)*

How old is the CTS? The green ones have been know to fail, don't rule it out. After that, there's the thermostat and poss water pump. The pump would be your last choise since you did say it was over heating. And the effort required to replace it. Go with the sensor first, it is a 2 part sensor, and apparently the half sending signal to ECU isn't working correctly according to the ECU.


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## dtgriscom (Feb 14, 2007)

*Re: CEL on, code P2181 (ps2375)*

Thanks for your note. The CTS is original with the car, so 4 1/2 years old. Given that the dash gauge works as it always has, and that the internal temperature is at least reasonable (I didn't mention that it reads reasonably close to ambient after the car had been parked for a while), do you still think it might be the (dual) sensor?
In terms of temperatures, is a peak engine temperature of 205F abnormal? After all it's below boiling, and that's before you add antifreeze.


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## ps2375 (Aug 13, 2003)

*Re: CEL on, code P2181 (dtgriscom)*

that is near what the thermostat will keep it at. And the system is pressurized, so the boiling won't happen till well above 212*F even with straight water. So, that sounds like the thermostsat and pump are working. Yah, I'd still go with a new sensor. It may be slow/intermitant to the ECU.


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## dtgriscom (Feb 14, 2007)

*Re: CEL on, code P2181 (ps2375)*

Thanks a lot. I'll get the sensor, and report on the results.


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## bras444 (Aug 21, 2006)

*Re: CEL on, code P2181 (dtgriscom)*

Let me know how it goes. I have the same problem. my CEL went off a month or so ago, i had the black sensor, so i replaced it with a new green one, erased the code and all was fine until yesterday. i got the same code p2181, erased it this morning, went to work and on my way home it went off again, same code. any help would be much appreciated!


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## SLVR SLUG (Dec 10, 2006)

my temp needle dies sometimes.. but the car never seems to act sluggish or show any signs of over heating.. could this be a faulty sensor also? or a wire problem somewhere between the sensor and the dash?


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## ps2375 (Aug 13, 2003)

*Re: (BlUnT MeKaNiX)*

prolly sensor.


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## dtgriscom (Feb 14, 2007)

*Re: CEL on, code P2181 ("Cooling system performance") diagnosis (dtgriscom)*

Well, I replaced the sensor ($43 from my local VW dealer: ouch.) Once I had the parts in hand, and the engine was cool enough, it took all of two minutes (less time than it took me to replace one of the windshield wiper's rubber; who designed that damn thing????). I then cleared the check engine light.
But! the CEL came back on. Darn, darn, darn, darn, darn. Being an optimist I cleared it again two days ago, but there's already a P2181 code pending, and I expect the CEL to come on again.
I guess I'll be making an appointment with the dealer.


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## ps2375 (Aug 13, 2003)

*Re: CEL on, code P2181 (dtgriscom)*

have you tried this? http://wiki.ross-tech.com/inde...08577 I would change the thermostat before paying dealer prices. you've got nothing to lose. The sensor usually cures this code, but apparently its not your sensor. 


_Modified by ps2375 at 5:57 PM 1-28-2008_


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## dtgriscom (Feb 14, 2007)

*Re: CEL on, code P2181 (ps2375)*

Well, here's the end of the story. I brought the car to the dealer, telling the service man that I'd found a p2181 code, I'd replaced the temperature sensor (his response: "good guess") and cleared the code, but the code came back.
They called about an hour later saying they'd fixed it. Dubious, I asked how: the answer was that they'd cleared the code. I explained that I'd already done that twice, and another time wouldn't help. So, they said the next thing to try was replacing the thermostat and coolant.
Still dubious, I asked if their scan had revealed more information than mine, and they said "no". I asked why they thought it was the thermostat and not something else, and they said that that usually fixed it. I asked what if it didn't, and they said the next thing would be the water pump. Continuing to be dubious, but not having much of a choice, I let them do what they suggested ($220, plus $100+ for the "diagnosis").
Well, I've had it back for two days now, with a fair amount of highway driving. I've watched the coolant temperature (I leave the Actron connected), and it does exactly what it's done all the time, with the exact same high temperature. Still no change in drivability, engine behavior, heater output, etc. But, there are no codes, active or pending. So, it looks like I'm finally fixed. Yee haw.
It's pretty annoying my engine computer will decide that something's wrong, but won't explain what the problem is even to the VW techs. In my mind there's a real possibility that this has been a wild goose chase, trying to find something that will pacify the engine computer, rather than fix a real problem with my car.


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## ps2375 (Aug 13, 2003)

*Re: CEL on, code P2181 (dtgriscom)*

well, the computer is just taking the inputs and doing what it is programmed to to with them. Sometimes it doesn't help you in the diagnosis, but their are a range of things it could've been. You start with the most obvious and easiest and go from there. The problem may not have been the actual temps, but the rate of change that was the problem.That is one of the few of those codes that was not fixed with the sensor. I'll have to keep it in mind on the next one. Sorry your's was stubborn.


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## modulation (Nov 6, 2006)

*Re: CEL on, code P2181 (dtgriscom)*

Hello.
I am having the same problem.
I think it is cooling fans.
Mine also work fine @ idle with the AC on.
However the cooling fans should go low-speed at a certain temperature (I think it's like ~85-90c) and mine don't turn on until my car reaches ~100 degrees C and it is the high speed fans I believe that kick on, and they shut right off when the coolant gets <100 degrees c.
If you would turn your AC off, let your car idle and then see at what temperature the fans come on..
I think I know what the problem is, but I'm not sure how to fix it yet.


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## dtgriscom (Feb 14, 2007)

*Re: CEL on, code P2181 (modulation)*

Well, three more days have passed, and no codes posted or pending. I think replacing the thermostat did it. Thanks for all the help.


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## modulation (Nov 6, 2006)

*Re: CEL on, code P2181 (dtgriscom)*


_Quote, originally posted by *dtgriscom* »_Well, three more days have passed, and no codes posted or pending. I think replacing the thermostat did it. Thanks for all the help.


I've spent hours searching and it seems that replacing the thermostat doesn't work for most people.
Like this dude:
http://forums.vwvortex.com/zerothread?id=2575529
Has it been warmer or colder the last three days then it was the week before?
Not to rain on your parade or anything but good luck.


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## dtgriscom (Feb 14, 2007)

*Re: CEL on, code P2181 (modulation)*

Seems to still be happy, even though yesterday was warm (coolant got up to its usual peak of 204F in highway driving). I think it's fixed.
Last observation: fixing this error code seems to involve a lot of trial-and-error, even by the dealer. If I hadn't replaced the temperature sensor then the dealer would have done so and called it "fixed", leaving me to deal with the re-lit CEL a couple of days later. So, my replacing the sensor and trying it certainly saved a pair of trips to the dealer (and their labor fee). Given how easy it was, it was certainly a win, even though it failed to fix the final problem.


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## Import_RaGe (Nov 29, 2004)

*Re: CEL on, code P2181 (dtgriscom)*

I had this code, my buddy tightened my gas cap and cleared it with VAG-COM and it went away. 
So in reality, I really dont know what fixed it.


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## Jhazon (Jul 12, 2005)

*Re: CEL on, code P2181 (dtgriscom)*

Hey dtgriscom, how's the code going? (update?)
I have a 2003 Jetta GLS Wagon and I, too, have this same code and have attempted to replace all items involving temp and cleared it a number of times. But it appears to be more of an idle problem for me. When idling I can hear/feel the car skip. When I use the cruise control, the car can be felt adjusting, more so than normal. I can even smell a different exhaust plus my fuel mileage is not very good. 
Any ideas?


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## Juancho9 (Jan 8, 2010)

*Re: CEL on, code P2181 (Jhazon)*

Sorry to resurrect an old thread, but Im basically having the same problem as described by dtgriscom. I replaced the CTS, but the code as stayed. I have it in the shop right now to be looked at. Before I took it in the mechanic said it sounds like the water pump, so Im hoping he doesn't say it needs to be replaced simply on a hunch, a quite expensive hunch at that. The only weird behavior Ive seen is that only on a few occasions my temp gauge wouldn't move. But after a restart it would be fine. Thermostat?


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## dnebs (Jul 18, 2011)

*P2181 - gas cap*

I tried the tightening of the gas cap and it hasnt worked. I am considering going and buying a replacement because when the tank is full the CEL is off. When it gets to 1/2 and below it lights up again. Then when it is getting close to empty, it turns back off making think it is related to that. 

Does anyone have any thoughts on that before I get into thermostats etc.?


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## gregersonke (Aug 25, 2011)

So a friend of mine had this issue P2181 with her 04 golf 2.0L N/A. I read through the forums online and numerous ideas came up. Flushing system, changing out the sensor, changing the water pump, changing out the fluid with a 60/40 mix. 

I found that it was easier to start with an obd2 scanner and monitor the temps. Discovered that the temps never exceeded 170, changed out the sensor for 10 bucks from Orielly. I still had the same issue, then figuring that the light was coming on due to never getting up to the 180f that the manual says this system requires. I got a 190f thermostat from an independent shop along with the new fluid and distilled water since I figured I'd be dumping out half the system anyways. You'll need a 3/8 ratchet with knuckle with at least 1 long extension and a short 10mm socket along with something to squeeze the spring clamp so you can remove the hose. Don't forget to put the rubber ring back in after you put the new thermostat in. Close it up, fill the secondary tank and start the car, slowly mix in fluid up to the min, turn on the heat and continue filling up for the next 5 min. Close lid on secondary, drive around, check fluid again and fill to min. Check the temp through monitor mode on obd2 scanner. Should read over 185f when car is warmed up. 

Whole process takes 2 hours and doesn't require a change of clothes.


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## Mat25 (Sep 6, 2011)

*P2181 code on VW Passat 2.0T, 2006*

I fixed my P2181 fault code on my 2006 Passat by changing coolant temprature sensor and it has been 2 weeks I am driving the car and the code did not come back again. I am going to attach some photo on where the sensor is located and try to read the thread on this page from other user about this issue as some of them are good to know before trying to change the sensor. Wait, I don't know how to inser the images here so contact me if you need these images so I can e-mail them to you.Good Luck.


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## tommydoo66 (Oct 7, 2009)

*P2181 thermostat was the problem*

The thermostat was my problem too after replacing the temp sensor. The key to the dx was stated in this post. The Engine was not getting to 171 degrees in X Amount of time or what ever the parameters are . My results were 167 degrees when the min.temp should have been the 171 deg by the time the computer has checked temp sensor reading. I did notice that the thermostat pulled was a lower temp of 180 not the oem temp of 192. I put the 192 in and new o ring . Used a 1/4 drive 10 mm socket with extension 9" and swivel right after the socket. Did not even have to remove the hose from the housing. 
Good luck




gregersonke said:


> So a friend of mine had this issue P2181 with her 04 golf 2.0L N/A. I read through the forums online and numerous ideas came up. Flushing system, changing out the sensor, changing the water pump, changing out the fluid with a 60/40 mix.
> 
> 
> I found that it was easier to start with an obd2 scanner and monitor the temps. Discovered that the temps never exceeded 170, changed out the sensor for 10 bucks from Orielly. I still had the same issue, then figuring that the light was coming on due to never getting up to the 180f that the manual says this system requires. I got a 190f thermostat from an independent shop along with the new fluid and distilled water since I figured I'd be dumping out half the system anyways. You'll need a 3/8 ratchet with knuckle with at least 1 long extension and a short 10mm socket along with something to squeeze the spring clamp so you can remove the hose. Don't forget to put the rubber ring back in after you put the new thermostat in. Close it up, fill the secondary tank and start the car, slowly mix in fluid up to the min, turn on the heat and continue filling up for the next 5 min.
> ...


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## Kam3152 (Mar 17, 2013)

*Still struggling with p2181 fix...*

RE: 2004 VW Jetta 2.0 
.................................... 
Hello guys 
I am new to this thread and do not know a lot about cars. All I know is what I've been forced to learn from trying to fix this awful p2181 code.... 

I found it interesting that so many of us have this same incurable code. I got an interesting diagnosis today, one that I have not read in anyone else's posts. Please tell me what you think. I'm a little skeptical.... 

But first, here's my cars back story: 

I have been living with p2181 for 3+ years now... My CEL light came on randomly one day and I just cleared the code hoping it was a mistake. A few days later the code came up again. After doing some googling,I decided to replace my CTS from O'riley auto parts ($10). A day later the CEL and code came back... 
The dash gauge has alway (and still does read a stable 190 degrees... ) I decided to investigate. I hooked up my OBDCOM reader via my laptop and drove around a bit. I could read the actual temperature from the OBDCOM coming in around 220degrees. I assume this high temp is what is causing the error code and CEL to come on? I turned on my heater full blast ( all the way red/hot & 4 fan speed). I could see the temp immediately drop down to normal range. I had a smog inspection coming up so I cleared the code and drove around with my laptop to monitor the actual temp and view the drive cycle process. (You will fail smog inspection with this code & an incomplete drive cycle). In order to complete the drive cycle and not re-trigger the p2181 CEL, you need to drive the entire time with the heater ON! I did this and passed easily. I recently took the car into a mechanic to have the thermostat replaced thinking that this was the next most probable cause. The mechanic did a series of tests to make sure it was the thermostat before replacing it. He tested the CTS with his instruments and that came back fine. He tested the fans, they were in working order, they took out and tested the thermostat and it seemed to be functioning properly ( hmm...) they also checked the coolant and it seemed to be fine. Annoying. Their final diagnosis was that my ECU (computer) has a bad "relay" that fails to initiate the "engine cooling system". I really don't have the money to replace the entire ECU 

Now to all you who know VWs, is this a probable cause for this error code. 
It seems like almost everyone is saying to replace the temp sensor and then the thermostat, but then again, there are a lot of people on here that say they have replaced those parts and are still getting the p2181.... 

I need help. If anyone has any good advice, please HELP 
Thanks


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## P23X (Sep 21, 2010)

*2006 jetta 2.0t*

I have been having this same problem. My P2181 CEL has been on since September 2012. haven't done anything to fix it as I wanted to try and get some feed back. I noticed that my passenger side (smaller) radiator fan does not spin. I tested it by turning the AC on high. Are both fans supposed to spin? I have read that only one will and the other will turn on if it needs to, and also read the opposite that both should spin. If both are supposed to spin... could this be the reason for the p2181 code since only one of my rad fans are spinning??

thanks


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## Anony00GT (Mar 6, 2002)

Kam3152 said:


> RE: 2004 VW Jetta 2.0
> ....................................
> Hello guys
> I am new to this thread and do not know a lot about cars. All I know is what I've been forced to learn from trying to fix this awful p2181 code....
> ...


This code is hardly incurable. I've fixed it countless times, and it's never been a bad ECU. The ECU can only passively monitor the cooling system, with the exception of the ability to turn the fans on.

Replace the thermostat and replace the temp sensor. Use good OE parts, not O'Reilly junk (cheap parts can result in this code, as well as others). This code comes up when there is enough of a difference that the ECU is not happy, but rarely are there any other symptoms. Replacement of both components fixes this code 100% of the time in my experiences. Sure you could sit there for days and test out the wazoo, but if the fans are working, these are the only two components that can cause this code and you have to drain the coolant either way. Drain it once, replace both. Fixed.




P23X said:


> I have been having this same problem. My P2181 CEL has been on since September 2012. haven't done anything to fix it as I wanted to try and get some feed back. I noticed that my passenger side (smaller) radiator fan does not spin. I tested it by turning the AC on high. Are both fans supposed to spin? I have read that only one will and the other will turn on if it needs to, and also read the opposite that both should spin. If both are supposed to spin... could this be the reason for the p2181 code since only one of my rad fans are spinning??
> 
> thanks


You're in the wrong forum, the 2.0T is a completely different animal. But yes, repair that fan and retest.


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## Kam3152 (Mar 17, 2013)

*Fans do not turn on*



Anony00GT said:


> This code is hardly incurable. I've fixed it countless times, and it's never been a bad ECU. The ECU can only passively monitor the cooling system, with the exception of the ability to turn the fans on.
> 
> Replace the thermostat and replace the temp sensor. Use good OE parts, not O'Reilly junk (cheap parts can result in this code, as well as others). This code comes up when there is enough of a difference that the ECU is not happy, but rarely are there any other symptoms. Replacement of both components fixes this code 100% of the time in my experiences. Sure you could sit there for days and test out the wazoo, but if the fans are working, these are the only two components that can cause this code and you have to drain the coolant either way. Drain it once, replace both. Fixed.



I just found out that the fans are NOT turning on when the car reaches the middle temp on the guage ( 190*) they do however BOTH turn on when I turn on the AC. AC works perfectly. Could this also be traced back to the crapper green O'Reilly temp sensor? ...Or dos this have to do with the fan relay/switch ? thank you !


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## Anony00GT (Mar 6, 2002)

Kam3152 said:


> I just found out that the fans are NOT turning on when the car reaches the middle temp on the guage ( 190*) they do however BOTH turn on when I turn on the AC. AC works perfectly. Could this also be traced back to the crapper green O'Reilly temp sensor? ...Or dos this have to do with the fan relay/switch ? thank you !


This is normal operation. The fan switch is different than the temp sensor, and the fans will not come on at 190*.

Temperature specification for radiator fan engagement low/high speed can be found in the service manual for your particular vehicle. The temperature must reach that spec at the fan switch (lower radiator hose or radiator, depending on what vehicle), not the green temp sensor. The green sensor is signal for the ECU and gauge, two sensors in one. It's not uncommon for the cooling fans to stay off until the temp gauge reaches near the 3/4 mark.


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## Kam3152 (Mar 17, 2013)

*Fixed...*

Thanks for the help. I took my car into Scott Wood. He evaluated the situation and ended up changing out the thermostat. It's been a week and I haven't had any problems and the engine light has stayed off!


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## Mannig (Jun 18, 2013)

*P2181*



Kam3152 said:


> RE: 2004 VW Jetta 2.0
> ....................................
> Hello guys
> I am new to this thread and do not know a lot about cars. All I know is what I've been forced to learn from trying to fix this awful p2181 code....
> ...


 Hello, 
I had the same P2181 cooling performance problem on my Golf 2004 with 2L engine. Changed thermostat and coolant .. Problem solved. P.s I use vw coolant and mixed it as directed.


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## SaskVW (Jul 24, 2014)

I'm having the same problem with my 05 Jetta 2.0 GLS. Mechanic replaced the sensor (they also showed an improbable temperature code which my OBDII never showed) and this code popped up again a few days later. After reading this thread it seems my next step is thermostat. I'm not sure if my cooling fans kick in or not, but my temperature gauge always seems to be in the middle. I'm not really in a rush to address this issue, but I will update this thread with my result. Das Aggravation. :banghead:


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## Anony00GT (Mar 6, 2002)

Scroll up and see my eariler reply. When I see this code, I usually verify that the fans work, and if they do, I drain the coolant once, and replace both the temp sensor and thermostat. Both cheap parts, easy to change.

Use OE parts too, aftermarket parts are often no good right out of the box.


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## SaskVW (Jul 24, 2014)

I dove it a bunch today and the temp gauge just sits in the middle so I don't even think the fans kick in unless it gets higher. On top of that It looks like the previous owner didn't even have the G12 coolant in. It looks like its yellow or orangish? definitely not pink. However it doesn't seem to have any precipitate in it so not sure if it was mixed wrong or what. Anyways I picked up a jug of G13 They said it replaced the G12. I bought a thermostat too. I figured I might as well change the thermostat and drain and flush the whole system. I have no idea what kind of coolant is in their or how it even will react with anything I put in there. Ugh... Used Cars suck!


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## Anony00GT (Mar 6, 2002)

Yes it may not get hot enough at idle for fan engagement, but you can turn on the A/C (provided it works), and the fans should turn on.

It's probably filled with generic "all makes/models" yellow coolant, blended with leftover pink G12 to make a yellow/orange color. That won't hurt anything.


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## Golf2quick0 (Mar 28, 2008)

SaskVW said:


> I figured I might as well change the thermostat and drain and flush the whole system. I have no idea what kind of coolant is in their or how it even will react with anything I put in there. Ugh... Used Cars suck!


When in doubt, flush it all out. If it's ever had anything in it besides G12, you're asking for trouble. 

I had this same code some time back. My issue was a failing water pump due to a broken/worn blade on the impeller coupled with a dying thermostat. Both were replaced when I did the timing belt service and I've not seen the issue return since.


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## jciancag (Aug 11, 2015)

*P2181 code on VW Passat 2.0T, 2006 (pics of Sensor location)*

Could you please send me the pictures you referenced in this post if you still have them (I realize this post is from 2011). I may need to replace my CTS and could use the help in locating on my 2006 jetta.


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