Scanning with the Canon mp620 with error code U163

Hold down the stop button for 5 seconds.

This will also work on the MX870, MX882 models.

Actually, I think I've found a solution! Fat-finger both the "STOP and "BACK" buttons at the same time. This seems to kick you out to the main menu.

Sorry for prematurely asking a question!

I got my MX882 back to working by pressing stop and holding it for 5 seconds. I got another error shortly after but then I pressed back and okay at the same time to get it working again. Hope this helps.