Fog build up on underside of glass plate.

It should not fog up. Has something been spilled on it? I would first try a hair dryer on it. But don't over hear anything

I recommend you do not take off the glass. I have done it and was never able to get rid of the dust, which really shows up on every scan. The fogging has something to do with an optical coating on the underside of the glass. If I knew then what I know now, I would let it be. If the fogging doesn't show up in scans, leave it. If it really does show up, the glass itself is often held down by simple double stick tape. You try to keep the tape intact so you can put it back down. It may be strong enough that the plastic frame on top of it could snap. Do it in as clean (not dusty) environment as possible so dust does not drift down inside the scanner. Never touch the lamp or move the scan mechanism. Again, don't do it unless it's showing up on scan results. Sadly, nobody "fixes" scanners, they are disposable, like coffee pots, even if they cost 300.00.

I clicked on this by mistake but this sounds like a call to Canon support would do the most good.Here is the number Contact Us at 1-800-OKCANON Hope this helps.

Down inside that scan assembly are mirrors and a lens, one cover to snap off. Try cleaning the lens, and mirrors, shining a flashlight straight down you can see a sort of fog on the glass. Also the white strip on the underside of the glass needs to be clean. After that you'll have to check around for a new scan assembly.

1. Remove the fog light mounting screw.
2. Disconnect the connector from the fog light.
3. Turn the socket about 45° counterclockwise and remove it from the housing.
4. Remove the bulb from the socket.

To Install:

1. Install the bulb in the socket without touching the glass with bare hands.
2. Turn the socket about 45° clockwise to install it.
3. Connect the connector to the fog light.
4. Install the fog light mounting screw.

hi from uk the fog lghts? i assume front fog lamps ? the head lights have to be on dipped beam then the fogs will also work but in uk this is so as to prevent fogs only being used (blinding oncoming traffic ) if weather conditions req fogs to be used for poor visibility ? then the side/tail and h/lights must also be on like wise the rear fog light/s operate the same way hope this helps and makes perfect sense ?? all above is assuming bulbs have been checked and fuse/relay and power to each lamp ?

You can access it from behind.You have to remove splash shield and go from the underside.

No problem.
1st step. Remove the lid. It just pulls out at the hinge end by lifting straight up, horizontal if you like. Where the two lid posts insert in the scanner body you will find 2 screws, undo them, no need to remove at this point, too hard. Rememeber you left them in there though.
2nd step. Around the 4 buttons at the control end is a striped trim panel that is the full width of the scanner. Locate the join between this trim and the light grey underside of the scanner body and just left and right of the COPY & EMAIL buttons, Using your fingernails lift with some gentle force. This edge will pop up. Note, the trim panel has 3 location tabs that insert under the grey border edge around the glass. So pop the front edge first and pull towards yourself.
3rd step. Once this trim is removed you will note 4 little grey plugs equally spaced under this area. remove the plugs and you will find 4 screws. Unscrew them, no need to remove, remember point above.
4th step. Time for CAUTION. You will be able to lift the upper part of the scanner up in which the glass is mounted. ***There is a lead with little play connected to the 4 buttons PCB which is attached to the upper panel. To ensure you don't damage it accidently when cleaning the glass you can remove the 2 screws attaching it to the upper panel.
5th step. See if you can wipe it, with a VERY SOFT LINT FREE cloth, without putting you finger on it somewhere......................
6th step. reassembly is the same in reverse

I would not worry about the underside of the glass unless you are having problems. The focal length of the ccd that captures the image is very specific and probably will not pick up anything under the glass. It is normal for the underside to look foggy but it will not hurt anything.