Fault codes P3081 & P2181?? (2005 997 C2)

Hi, Please can anyone help with some advice? I seem to have an intermittent message cropping up on my dash. The message on the dash says Temperature Indicator Failure, the temperature gauge stays at the bottom mark and the temp red light at the top of the gauge flashes. Clearing the fault code clears the issue for a day or so and the gauge reads as normal, The codes coming up are P3081 and P2181. From researching it on the internet it could be the; 1) Coolant Temperature Sensor or 2) Thermostat or both? Have you any thoughts on what it could be?? Thanks Chris 2005 997C2

I had this problem on a 997.1 S it took awhile to find but it turned out to be a very small leak of coolant from the offside main coolant pipe just above the drive shaft. The car would leak a small amount of coolant (a cup full) that would cause an air lock and stop the circulation so confusing the temp sensor and throwing up the code for thermostat fault. Its worth getting on the ground to check this pipe, lean under the car with a torch and follow the offside drive shaft towards the gearbox then look above it for the aluminium pipe, if you see a pink stain where the pipe goes through a plastic clip that could be your problem. unfortunatley we had to remove the engine to replace the pipe, the parts aren't expensive though. when the fault occurs and you loose your temp gauge, top up the coolant allow it to run at idle upto temp until the front fans kick in and your gauge should clear itself.

Wow remove the engine! Hopefully it's not that then..

Sorry, just realised I painted a scary picture, if it is as I described it's not the end of the world, but it is better dealt with before any overheating problems, got my fingers crossed for you.

Thanks a lot for your help.

Hi. I have this exact same problem right now on my 2005 997.1. I am going to check the pipe as Bryan suggests. Will let you know! Chris, did you solve the problem? What was it?

Right, no sign of leaks on Bryan's pipe. Also just idled the car for at least 20 mins and radiators fans did not deploy; radiators aren't even hot! I know the car's not over heating though. I also have connected (but not fitted) a new temp sensor but this does not clear the fault. I think I will delete the fault using the diagnostics and see if it comes back immediately. If it does, new thermostat and housing?

Hello Jules, that’s good that you don’t have a leak on your pipe, have you lost any coolant at all? having run the car for twenty minutes I would expect some heat in the radiators so maybe your thermostat is not opening (fully), the temp sensor connected but not fitted may confuse the issue. I would reconnect the current fitted temp sensor, clear the codes,run the car from cold, watch the water temp rise on the gauge, check the radiators (bare in mind the front rad is for air con son won’t get hot), if you have not heat at your radiators your temp gauge will quickly go over its normal range and more than likely your thermostat has not opened. a good place to monitor the temp of the circulating coolant is at the rubber pipes in the front wheel arches. good luck

Hi Bryan. Thanks for this. Exposed as a 911 newby! I had no idea there were two rads each side, one in front of the other. OK, that explains that! No coolant lost no. The original temp sensor is reconnected (I connected the new one to see if it was just a sensor fault) but I can't watch the temp gauge rise as it's not reading anything and the red light is flashing, just like Chris's first post on this thread. When this first happened, is corrected itself after about 10 minutes. Then it happened again, and now it seems more permanent. Each time it corrected though, temperature reading was spot on, hence my belief the car is not overheating. So on that basis, I am still driving the car (it's my daily driver). Hope I'm not damaging it! I will clear the codes tomorrow and check the rubber pipes after running as you suggest. Will let you know the outcome!

Hi. So codes erased, temp gauge now working, pipes warm and fans kicked in after about 15 mins idle. All looks good so far. So if this is an intermittent fault, I wonder how long before it comes back. Will post here if it does. Thanks Bryan for your help in the meantime.

[FONT=calibri"]It's a long time since my last post, but at last I found time to look further into this problem, which came back with a vengeance. In fact, the only time the fault disappears it seems is when idling and the fans are needed. [FONT=calibri"]During a long motorway drive, on an occasion when the temp gauge was actually working, I notice that temp was restored to 80 degrees powering up hills, but dropped down when coasting down hills, eventually to the point where the fault reappeared. Whenever the fault clears and the gauge starts working again, the temp is always back to 80 degrees. So my view was, and still is, the fault was that the engine temp was too low and there was no overheating at any time. This smelled 100% like a thermostat which was stuck open, so based on the advise in the thread above and other investigations, I set about replacing the thermostat. [FONT=calibri"] [FONT=calibri"]This I have now done, also replacing the brownish (!) old coolant fluid and the temp gauge sensor. The old fluid, whilst brown, had no particles in it, was clear in colour as it was being poured, and did not really look like corrosion. So perhaps it was just a mix of antifreeze from before I owned the car that maybe reacted? Opinions welcome on that. But I am hoping this is not the sign of something more sinister. In any case, I will change the fluid again in the summer to see what colour comes out then. [FONT=calibri"] [FONT=calibri"]Anyway, having done all the work, and refilled the system with new coolant, it has not solved the problem. I cleared the faults and whilst test driving, the exact same symptom reappeared. Costing down a hill, temp dropped from 80 degrees, fault warning with temp gauge down to zero (or 40 in fact as that's the lowest it goes) and temp warning light flashing. The on board computer says "Engine Temperature". On hooking up the OBD, I however only get one fault this time: "P3081 - Manufacturer Specific" (not the "P2181 - Cooling System Performance" I got last time and that Chris Hill got when starting this thread), but for the life of me, I cannot find anywhere what this means for a 997. The only Porsche lists I have found stop way short of that number and the only other place I have found it is for a VW where it means "Ambient Air Temperature Sensor Circuit Low", whatever that means. I am wondering if there is an air lock in the system which might be causing the problem. I have ordered a vacuum bleeding kit which I will try once it arrives just to try to make sure there is no trapped air. [FONT=calibri"] [FONT=calibri"]If anybody has or can point to further information on what P3081 is, or can provide any other clues, I would be eternally grateful. [FONT=calibri"]Chris Hill, did you solve this? [FONT=calibri"]Otherwise, it's going to be a trip to Porsche, itself a 2 hour trip to the dealer from where I live! [FONT=calibri"]Many thanks, Jules

Happy New Year all. Now the festive season is finished, I decided to do some more research on this matter and found a very interesting article on Rennlist here: https://rennlist.com/forums/997-gt2-gt3-forum/614335-again-cel-2.html This basically describes the "unnecessary replacement of coolant regulator and temperature sensor" when "Display (temp gauge) only works sporadically and the following fault memory entries in the DME control unit: P2181 – Thermostat stuck open P3081 – Engine coolant temperature implausible" It suggests a blocked disc valve (on transmission housing) as a likely cause and that this should be checked (visual inspection and function test) before replacing the coolant regulator and/or temperature sensor. Being the sort of person who values time more than money (within reason) I have ordered the new part (928.574.573.03) and will swap it out irrespective to see if this solves the problem. In order to avoid draining the coolant again though I have had to also order some pinch-off pliers (to pinch and seal the hoses either side in order to replace the valve) which wont arrive for a few weeks, so next update after that. Wish me luck!

Jules, Just an interested observer, but in case you missed it in the text: An indication of a defective disc valve is also if the oil temperature and coolant temperature are almost identical in the warm-up phase. As a rule, the coolant temperature should be higher than the oil temperature. If you've not yet checked this out it would be worth doing while you're waiting delivery of the part and pinch-off pliers. Good luck with getting it fixed after all your efforts. Jeff

Hi Jeff, Thanks for that and yes, I had already noticed that when the water temp is low, the oil temp is also low; I was keeping an eye on oil temp as I had no indication for water temp! Of course it doesn't help that when you get fault P3081, the temp gauge on the dash is switched off completely by the ECU, presumably so as not to give a potential false reading and false sense of comfort to the driver. That said, I would have thought the constantly flashing warning light would be sufficient! Anyway, thanks for the tip. Jules

Sorry to be the only one posting here at the moment! Further update. Today I inspected under the car while I await the delivery of my new hose pinch off pliers. I checked the operation of the disc valve on the car as it struck me it could get fouled my mud or something getting caught there, but it seemed to open and close by finger pressure as I would expect. I then started the car, expecting the valve to close (by vacuum) to assist the warm up but it did not. Can anyone tell me if the disc valve should close on starting? Further, I noted that the vacuum to close the valve comes via a 3 piece pipe/hose combination from the Change-Over Valve, which then also begs the question whether this valve is working properly or if the hoses/pipes have a leak. Anyway, I will change the disc valve as planned when the pinch off pliers arrive and see what happens. Next step if that doesn't work will be the change-over valve and pipes that provide the vacuum.

Jules, According to this thread the valve should be closed at idle: https://rennlist.com/forums/997-gt2-gt3-forum/905174-disc-valve-on-transmission-operation.html Maybe you can check whether or not you're getting any vacuum at the valve for different engine operating conditions and temperatures? Jeff

[FONT=calibri"]Thanks Jeff for your last post. Here is the latest. [FONT=calibri"]Today I replaced the disc valve to no avail. I checked the vacuum on the exit of the change-over valve on cold start idle and discovered I have none. This raises several possibilities: This could be correct. However, I can’t believe it can be and it seems to contradict what was said in the Rennlist post above. Surely anyway the valve would be closed on cold start up as a) the ATF does not need cooling and b) a smaller coolant circuit allows the engine to warm up quicker; something it’s not doing! I have not yet checked at other temperatures as I want to check the following things first and in any case, I still get the fault. There could be no vacuum arriving at the changeover valve. I should have checked this today but it seemed more difficult to do as the input hose is behind the valve. I have since discovered it simply unclips so I could maybe check that tomorrow. However, I thought I would check whether the other end of the hose is connected to something (or if it has simple come off or is damaged) and whether there is vacuum there. Does anyone know where the other end of this vacuum hose can be found? The change-over valve could be broken. I could replace this anyway but that's another delay and potentially ordering parts I may not need. I would rather prove vacuum is arriving as it should at the change-over valve first. The change-over valve may not be switching i.e. an electric fault somewhere (cable, contacts, valve itself broken, source). I assume this is switched by an ATF temp gauge. Can anyone confirm? [FONT=calibri"]Tomorrow I will try to check the vacuum at the change-over valve input but if anybody knows the answer to the two questions above I would be most grateful. [FONT=calibri"]Thanks, Jules

Jules, Have a look at this PET for your car (2005 997.1 Tip?): https://www.porsche.com/all/media/pdf/originalparts/en/E_997_KATALOG.pdf You'll probably recognise some parts in sections 107 (throttle body) and 360 (TIPTRONIC, atf cooler, atf lines), but I think you're going to have to trace the vacuum lines by hand and check that you're actually getting a vacuum at the disc valve line at some stage of your warm-up. I'm not sure whether or not it's relevant but note that in addition to the change-over valve at the transmission (item 13), there also appears to be a similar device at the intake distributor (item 12). That's the problem with modern cars - too damn complicated for their own good..! Keep going - I'm sure that you'll get there in the end. Jeff

Hi Jeff, Thanks for the PET! That's immensely useful. I have been under the car again tonight and can reveal the vacuum pipe goes along the gearbox case and somewhere into the top of it! I needed an endoscope to see it and even that was tricky. Thankfully, I then did a vacuum test at the input of the change over valve and hey presto, about 1 bar of vacuum. So, my belief, is that the change-over valve has given up and my next step is to order a new one and fit it. If that doesn't do it, then it must be electrical i.e. the change over valve is not being switched. That would be a whole other kettle of fish that I think Porsche would have to sort out. Anyway, will order the part and post when I have fitted it. Thanks for your support! Jules

Sounds as though you're nearly there Jules. Maybe it's just a bad electrical connection at the change-over valve? If that seems OK then it might be worth checking that you're actually getting a voltage at the valve before investing in a replacement. If the valve's not being activated then, as you say, it's probably time to see if Porsche diagnostics can help. Jeff

Hey Jeff et al. I had ordered a new change-over valve anyway so tonight I fitted it. Before I bolted everything back together I started the car ... no beans. Then I noticed the fault was still registering, so I hooked up the computer, cleared the fault and hey presto, disc valve closed when I started the engine. Warmed engine to 80 degrees and it seemed to warm up much faster than before, which is what I would expect. Interestingly, I noticed that the brand new disc valve I had fitted was leaking! So I also had to put the old disc valve back on. Bit annoyed about that and will definitely be sending the new part back. It's bad enough when you are doing exploratory diagnosis and you don't know what you're doing, but when you get duff new parts too, that's a nightmare. Always something to bear in mind though! My wife has made me promise not to say i think it's fixed but ... that is the first time I have seen the disc valve closed so it's looking promising. Will go for a test drive at some point tomorrow to see what the final verdict is. Wish me luck! Jules

Hi Jules, It sounds as though your persistence has paid off and that the problem was due to the faulty change-over valve. Disappointing that the new disc valve was leaking, but you should be entitled to a refund. Hope all goes well with the test drive today. Jeff

FIXED!!! [ ] Test drive yesterday looks very much like this issue is now fixed. Took the car for a drive yesterday and noticeable differences. Car now warms up much quicker, does not cool down when engine is under load, does not cool down when coasting down a hill, oil temperature higher and of course, no annoying warnings! So, to reiterate, the "System Fault" warning appeared on the dash (with the red "!" warning light), the temp gauge stops working and the red temp warning light flashed at the right end of the temp gauge. When I connected up the OBD I got fault codes P2181 ("Cooling System Performance") and P3081 ("Manufacture Specific" which in the case of a 997 means "Engine coolant temperature implausible"). On occasion the fault would clear itself and the temp gauge would then read spot on 80 degrees. After clearing and before the fault appeared again, the temperature would always go down before (I guess) it reached a tolerance limit and the fault occurred again. The problem was under-heating as opposed to over-heating. As the car was under-heating, the obvious place to check was the thermostat which sends water to the radiators (or not), so I changed this first based on various advice found during a quick Google. I am glad I did this as it required me to drain the coolant, which obviously had been mixed during it's life and needed replacing. This work however did not solve the problem. I next read this thread which suggested the disc valve, at which point another cooling circuit came to my attention, that which cools the gearbox oil. The disc valve opens up the channel to a heat exchanger / radiator which cools the oil and this is located under the car where it gets a lot of air, so it's very efficient. What became clear was that this circuit was stuck open i.e. the cooling was permanently on. This equates to the disc valve being in its "rest" position (it's spring loaded), which is as it is when the car is not running. As soon as the car starts (from cold), this valve should close to aid warming of the engine and as obviously the gearbox oil does not need cooling at that point. The way it works is that an electrical circuit (I assume triggered by the oil temp sensor) opens the change-over valve (next to the disc valve), that in turn directs vacuum to the disc valve. The disc valve then closes as a result of this vacuum thereby closing the coolant circuit and stopping the oil cooling. I could have done better in my investigation here (I should have checked vacuum first) but my next step was to change the disc valve, to no avail. I then checked that I had vacuum into the change-over valve (which I did, lots of it!) after which I changed the change-over valve. NOTE: YOU NEED TO CLEAR THE FAULT CODES BEFORE THE DISC VALVE WILL WORK PROPERLY AGAIN! At first I thought it still wasn't fixed but clearing the fault did the trick. I started the car and saw the disc valve closed for the first time. So there you have it. If you get these fault codes and the same symptoms as described above, I suggest you first check whether the disc valve changes position when you start the engine from cold (you can do this with the car in the air without even removing the under tray; there is a convenient hole to inspect through). If not, this is your problem. It may not be the exact same fault as on mine but at least you know where to begin your investigation. Happy to answer questions on the procedure if anyone has any. Wasn't easy with the restricted space but then again, what is?! Thanks so much to Jeff for the moral support; couldn't have done it without you! Jules in France

That's great news Jules - your persistence finally paid off. Happy to have been a sounding board for your efforts and hope that your experiences will be of use to others with the same or similar problems. Happy Porsche-ing..! Jeff

997 Turbo 2008 Exactly my problem it appears! Will read Jules posts and Jeffs comments AGAIN before doing anything! Thanks