I wondered what would happen if I accidentally pressed P while moving. A couple times while not quite stopped at the mailbox, I did this and it stopped abruptly! What if I was REALLY moving . . . tried this in the long driveway. Found that above about 2 mph nothing happens . . . button doesn't light, car keeps going. If I'm down around 2 mph, then it stops. Conclusion is that I don't have to worry about pressing it while going 70. FYI Don
In my generation (gen 3), above the speed where it goes to park, I think it just beeps and goes to neutral.