Auto focus doesn't work...

Old Canon DSLR camera tech here. I know I'm really late to the game (by about 5 years), but if you still have the camera and want to try cleaning out the AF unit, it is inside the camera, on the bottom of the mirror box. IIRC, the reason the camera works fine in "M" (Manual) mode is because the autofocus unit is not engaged while in the "Manual" mode - your eye and judgement are used for focusing.

Please do not attempt any de-soldering unless you're very familiar with the process - you could ruin the electrical lands & traces, ultimately ending up with a dead camera...

Take any lenses or covers off the EF mounting ring, move the mirror assembly up and secure it in the "open" position (use a piece of tape or hold with a finger). Then turn the camera upside-down, and blow short blasts of air into the AF unit (you should see a diamond-shaped configuration of holes resembling the 9-point autofocus you see through the viewfinder). Don't use any liquids (even isopropyl alcohol) in an attempt to clean it - only air!

Once you think it's been cleaned, put it back to its normal configuration and try again. If that doesn't work, you might try a few more times, but the AF units can go bad - I've replaced more than my fair share. As far as I remember, they are replaceable and do not require any special calibration. If you can source an AF unit for the camera, please follow the disassembly instructions already here on the site, to the point where you remove the tripod mount. After that, you should see the boxy black plastic of the AF unit. I believe it's held in with two screws, although the lead cable will also need to be disconnected from the mainboard. Try to get the replacement unit as perfectly squared as possible to ensure proper AF function...

Or, contact Canon and see if they will fix it, and how much they'd charge.