I have a customer with an HP Laserjet 3380 all-in-one printer that when he turns it on it goes through the normal warmup, moves the scanner all the way to the left, makes a grinding sound and displays "scanner error" with no code number. I have looked through the HP support forums, but do not find a matching symptom to give me a clue. Any suggestions?

Most HPs have a built in scanner lock. Is the scanner lock engaged? Have you watched the scanner home? Does the scanner strike any obstacles on the way to home position?

you need to check the rail bushings one has a crack in it or a bad spot on the rail

These machines are noted for this fault....There are about 8 to 10 screws to remove the top glass, some are inside the side covers, some come up through the bottom side of the scanner top half, but make sure you remove them, dont pry, it is not snap together, the op panel cover does snap off, then there is a latch that prevents the op panel from sliding to the right, hold down on that tab, slide to the right and lift & unplug the op panel, there is screws under that panel and on the front. once you remove the top glass, clean the scanner rail & lube it, clean the white reference on the underside of the glass, that is where the problem is, the scanner cant read where it should be, so it just keeps driving. also clean all the mirrors in the scanner unit. This should take care of the problem. Let us know how you make out.
Brian