I have a strange situation with my 2008 Turbo Coupe. The car is lowered on H&R Springs. The wheels have the same spec as stock except the rears are half an inch wider. When running with Sport button on and PASM button on or off, I have no issues at all. When running in the default mode of sport off and PASM normal, I get the following fault message .

"PTM briefly inactive, too hot." The fault appears within 10 miles of shutting off the sport button. I can make it repeat every time. The fault will disappear for a few minutes and then return. I assume the module is inactive until it cools and then works again until it gets too hot. So every 15 miles or so it pops back up.

From what I understand, the PTM manages power to the front and rear axles. Why would it overheat in default mode, but not sport? When I get this fault does it mean I don't have power to all wheels or do I just lose traction control?

The car is headed to the dealer tomorrow morning, but they sounded stumped over the phone. They said they've lowered dozens of cars with the H&R setup without any issues.

 

It's your rear wheels, not your springs. I read about this strange occurence on Rennteam a while ago and can't quite recall the exact explanation. But it has something to do with torque to the PTM. You might want to search on Rennteam. If you replace your rear wheels with standard size wheels, the problem will go away.

 

Thanks. You are correct. The rear wheels are 1/4" larger in circumference. That's all it took to throw the PTM off. The different RPM's of the front and rear create more friction and the PTM fluid overheats. The dealer is installing stock tire sizes on the rear tomorrow.

 

Isn't it scary how I know more about Porsche 911s than the mechanic, yet I don't know shit about how to fix a car?