A few years ago the temp sensor fell out of its mount and as such the fan would run for quite a while, even after short trips. Thanks to a tip read here, I was able to find it and put it back where it belongs. Problem solved.

Now it's doing it again, but sensor is in correct place. Is temp sensor bad?

 

Could be shot or just a bout of very hot weather? (you probably took that into account already though...). Pretty inexpensive part (if you don't insist on the Porsche branded one)... http://www.autoatlanta.com/porsche-parts/hardparts.php?dir=996-99- 05&section=107-10

 

could you share a picture of where that sensor is located?

 

Part #8 in this diagram http://www.autoatlanta.com/porsche-p...section=107-10 it sits in a rubber grommet in between the intake runners on the bank 2 intake plenum

 

It is basically a heat activated switch. Unplug it. Does it shut off? Yes. Jumper the pins on the harness, does it turn on. Yes. Your switch is bad. Or vice versa, I can't remember exactly. Either way troubleshooting takes all of 2 minutes.

 

Thanks all! I'll try your suggestions.