Last week, my PEM decided to give up the ghost as I was driving down the highway. I got a "Powertrain Fault" which shut down power, and I coasted to the shoulder. I tried shutting down the car and restarting. The fault was gone until I let off the brake and touched the accelerator in which case the fault came back. Called Roadside assistance and they towed me home. I uploaded loaded logs to Tesla, and the next day they arranged to send out a Ranger to my home on the following day (he had a 6.5 hr drive from Chicago to get to me).
When he got here, he checked the battery, motor, motor leads before condemning the PEM. So he changed out the PEM with a replacement and everything was good to go again. He checked the cooling fans and they seemed to be OK, though he did blow a lot of dust out of the back end of the car (I live on a gravel road, and have about 2/3 mile before I get to pavement). Looking at the PEM, its sealed where the leads enter and no dust was evident inside the connection area. The inverter portion receives cooling air from the fans, and while dusty didn't look too bad to me. I don't think dust caused the failure since the sensitive electronics are sealed. The cooling fan for the motor blows air into a duct that surrounds the motor, and thus never puts any air into the motor housing.
Overall, I'm very happy with the Roadside assistance and customer service from Tesla. I'm curious why my PEM failed, and am not sure if I'll get any feedback from Tesla on the cause of the failure.