I wanted to post this in case it helps others.
My sliding door would not stay open, and since my driveway is on a slant, it was rather annoying.
I did lots of searches, most coming up with threads about the door getting stuck closed (which I also had problems with). Anyway, I found one note that got me going in the right direction.
The doors have a latch at the bottom front that is supposed to catch when the door is fully open. The posts I saw suggested that there might be a rock or something blocking the latch.
I checked that, but it was a no. But while messing with that latch I discovered the cable to the latch was frozen/stuck. I was able to remove that cable, and with some penetrating oil and some patience I got the cable sliding smooth again. Re-installed and presto. Door stays open.
Love no cost fixes.