make sure the scanner lamp is comming on.. If not scratch the rest and take to a copier shop.
You will have to take all the lower skins off, the wiring to the scanner unit are under these skins, then there are a few screws that allow the scanner unit to move to either the back front or the side once removed, so the scanner can be removed from the print portion of the machine. Label everything. Once off, the screws that allow you to get into the optics are on the bottom of the scanner, the bottom comes off(up side down) then you flip over, and dissasemble the scanner unit... which are a bunch of picky mirrors(dust free rag, and no streaks)... once you pull the mirrors out and clean, clean the scan slit glass, and the main glass, also, there is a white plate under side of the scanner top skin... this white plate lets the machine see true white... if it can't read a measurable true white, then it throws a code, so clean the white plate just the same as the mirrors. Also make sure there is no dust on the lense inside the scanner unit(looks like a camera lense) do not touch the lense if you don't have to, just blow(spitless) on the lense if you can to remove any dust.
I have worked on this machine before, and even an expierienced tech it takes some time to go through.. prolly about an hour for the whole machine. You might consider taking it to your local printer repair shop.. Most give a 50-100$ initial cost without parts... since this seems to be a no parts issue, it should be cheep