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

JulesInFrance · Jan 18, 2018

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

Motorhead · Jan 19, 2018

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

JulesInFrance · Jan 21, 2018

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

Motorhead · Jan 21, 2018

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