I have not found auto park to be a very reliable feature of my 2017 model S so I have not really used it since last March. However, yesterday, the auto park prompt came on when I was backing into my space in our hospital parking structure. . Though I was already halfway into the spot when I initialized auto park, it worked fine, stopping several inches before the wall behind me. The auto park prompt came on again this morning under similar circumstances, so I let it try it again. Luckily I was paying close attention because after I initiated the auto park function I noticed that the car was moving alarming fast. As soon as this dawned on me, I quickly hit the brakes, but in time to allow my rear bumper to touch the wall of the garage behind me. I did not sustain any real damage except for a bit of white paint on the bumper. Interestingly, the "stop" warning was showing on the panel and sounding the warning ping in front of me as well. I called Tesla and asked them to download the log from the car so they could see what happened. This glitch in auto park could have resulted in actual bumper damage or worse if I didn't catch it in time.