When using the document feeder for copying, faxing or document scanning, and you begin to get a line on your print outs, it's usually time to clean the glass.
If you raise the document feeder you will see two glass areas. One large one that we use when hand registering a document on the glass, and a small one along the left side of the optics area. It is this smaller slip glass that needs cleaning from time to time to keep lines from appearing on your documents
Finding the spot can be challenging, so here's a tip: take the copy with the line on it, and place it face up on the large glass as if you were about to copy it. The line on the copy will point to the spot on the smaller glass that needs to be cleaned.
Clean the area with the provided cleaner cloth, or a damp paper towel. Don't be afraid to apply a bit of pressure to clean the area thoroughly.