About a second into hard acceleration from a start from a freeway on-ramp limit light (I was trying to beat a BMW 3-series), a loud "BANG" came from what seems like the drive unit part of the car, then the car coasted to a stop while I could still make the motor whirr (I could hear it) using the accelerator pedal. I used my remaining momentum uphill to pull to the right shoulder in the combination on- and off-ramp while turning on my hazard lights. So from the car I called up Tesla Costa Mesa Service, just because it was easier to find in my Contacts, to report the problem. They connected me to Tesla Roadside Assistance too. It was almost 6 pm on a Wednesday, the freeways clogged with traffic, so they estimated a half-hour for the tow truck and the loaner Tesla to get to me. Ironically minutes earlier I celebrated the fact my S reached 25,000 miles exactly, taking a picture of my dash. I never perceived any "milling sound" or any unusual behavior prior to this sudden failure. I'm not aware of any changes to my drive unit since taking delivery back in February 2013. I also just picked up my 3-year-old daughter from preschool, so I tried to entertain her as cars roared by on our left. This was not a a safe place to be, and a wider shoulder was just 100 yards ahead, but I had little choice because I couldn't move the car. With some time to experiment, I put it back in drive and could hear the motor quietly whirring whenever I pressed the accelerator pedal, with a corresponding few kW increase in orange energy consumption, but the car would not move. I'd guess the problem was a gear or a gear idler broke due to metal fatigue. When I let the motor rotate very slowly, I felt a very loud very low frequency (~10 Hz) rumble, which suggests to me gear teeth or a broken shaft is rubbing. All other components (the battery pack, steering, etc.) continued to operate fine. The tow truck arrived first, and he hooked up my car to his tow truck while dodging traffic. A few minutes later the loaner Tesla arrived, and I quickly transferred by daughter, by kids' carseats and other belongings to the loaner. The tow truck driver directed me to take the loaner and my daughter away while they deal with my car. I gave my daughter McDonald's to make her happy after this emergency. The next day I visited Tesla Costa Mesa via the loaner say they were locating a replacement drive unit. I could see my car up on the lift but the old drive unit was out, with no visible external damage. Today they said they installed the replacement drive unit and plan to road test it and break-in the drive unit, then drive it to me and take back the loaner Tesla. I don't know if they'll every tell me what part failed. I feel fortunate the drive unit Infinite Mile Warranty announcement came just in time for me. I agree with Elon Musk that it's better just to replace the whole thing and return the vehicle, so Tesla can take what time they need to investigate or refurbish the old drive unit. It's a lot like AppleCare replacing the whole iPad or MacBook Pro rather than make the customer wait to repair "that one". Even though the failure was sudden, I feel I can put this in perspective: my previous car, a 2001 M3, had a recall replacing bearings and piston rods. I read that others' engines essentially tore itself apart at speed because the bearings seized. If that can happen to BMW, it can happen to any carmaker, particular with high-performance cars like the M3 and S P85. In retrospect the M3's issue seems much more dangerous (for me) and complex (to service) than this one. Carrying out this BMW recall took Long Beach BMW a whole week, mostly to rebuild my M3's engine. Tesla is returning my S 40 hours after the incident, so I cannot complain. Today I will have a whole new drive unit (my first replacement), like when Tesla replaced my battery pack early this year: Tesla Stands by its Battery Pack Warranty With the pack and the drive unit being fundamental to this EV, like in Theseus' Paradox: Ship of Theseus - Wikipedia, the free encyclopedia how much more needs to be replaced before it's essentially a new car?