Dell 1600n printer, how can I clean the platen glass?

Take the printer apart. It's usually less than 8 screws. Clean theback of the glass .... Bingo ..... Also google the Dell model printer. How to take apart a bla bla printer. From. Google.com.

Clean the platen glass with a softh cloth. Obvious, Isn't it?

Do you get the same line when you use the adf for other purposes?

If so, check the scanner glass just before the platen for something like white-out on it. Clean both the scanner glass and platen glass with Windex.

That is a common problem on all ADF scanners.

Good Luck

Found the solution at http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=SupportDetailTabAct&fcategoryid=239&modelid=13170&kbpage=yes , then enter "clean platen glass" in the search window, and select item #1 "ERROR LCD: PLATEN GLASS DIRTY, CLEAN PLATEN GLASS ". This gives step-by-step instructions on how to clean the area dealing with the platen glass.

Clean the small glass, even the slightest dot, it will interpet as a line.

It has to be taken apart, but should not get dirty by itself, it's pretty much sealed. Try cleaning the top again. If not let me know and I will try to find the dissasembly instructions for you.

If it makes verticle lines only when using the document feeder it is most likely a dirty glass strip over the scanner light bar. If it makes verticle lines in all modes (printing, flat bed scanning/copying, receiving faxes) it could be the fuser or a dirty glass over the laser where ever the laser images to a drum roller (usually a larger green roller). It is possible that this green drum roller is inside the toner - if so - replacing the toner cartridge could fix it. Maybe you could try an old used toner to see of the problem changes - if so - it is very likely that a new toner would fix your print quality issue.

Clean the small glass strip on the left side of the scanner. There is probably some dirt there and will only show up when using the ADF.

There are 2 seperate glass areas on the top, the large one is for when you lift the cover to scan or copy, the little narrow one is when you use the ADF. If there is a dot or a spec on the narrow part, it will leave the streak on the page, Clean the narrow part really well. I use a foaming window cleaner, and a razor blade.
You may also want to check to see if there are any small scratches on that glass. That will cause the same thing to happen.

You have either a piece of dust or a scratch on the scanning glass. This will show up as a line because the paper is pulled across the point.