I have a year 2000 C4 tiptronic. When it's been run for a while and is hot, it cannot be restarted normally, after being turned off. The solution is to force the transmission out of Park to Neutral (and it does require some force). In Neutral it will start. My Porsche service people have not been able to fix this, probably because it's hard to replicate. Has anyone seen this problem, so that can give the Porsche service people a pointer?

 

I don't know if this is your problem... but, there is a sensor for the ATF cooler that can shutdown the Tiptronic program if it senses the transmission ATF is too hot. If this sensor were defective (or if your ATF is really too hot) I think it will shutdown the Tiptronic drive program and may not allow re-starts. Has your dealer done a PST2 fault readout on the transmission?

 

It sounds like the PnP switch to me. There is a switch on the transmission that prevents the vehicle from being started while in any gear but N or P. It sounds like once the the switch gets hot the contacts do not close in the P position, but they do close in the N position. Which would make sense, because P is used more frequently than N and they are probably more worn. Just my $.02

 

I may get in trouble here implying any semblance to an Audi but my girlfriend had a similar problem on her '02 Allroad. The car wouldn't start so she called the dealer and the service guy told her to force it out of P and into N. The car started in N but she reported it ran rough until she got it to the dealer. This was probably the quattro (TCM fault) trying to figure out where it was.

Audi replaced the TCM (trans control module) which is a known problem on these cars. The kicker is they also had to replace the solenoid that prevents the car from coming out of P at the wrong time. They claimed a "voltage spike" from the TCM that caused the solenoid to fail. I don't believe a digital device (TCM) can take out a solenoid (big fat wires). I believe the solenoid/lock-out mechanism was damaged from when she followed instructions to pull (hard!) out of P.

So, based on my theory, I'd first check if that locking mechanism is operating smoothly when cold or hot. Try, ignition on, foot on brake, then it should go from P-N? If that is so, then see if that solenoid is getting the proper signals from whatever the equivalent computer is in the P-car.

Bottom line, whatever repair they eventually perform, it might be worth having them check that mechanical stop for damage.

Good luck,
Andy, C4S waiter(!)