If the line that is being produced only occurs when using the Automatic Document feeder (ADF) and not when making a copy via the platen glass, the issue is commonly due to a small mark or debris on the scanning glass area that lines up underneath the white vertical ADF roller. A small smudge on the platen glass can cause a "line" to be produced as every inch of the paper fed via the ADF passes over the area and is picked up by the scanner. The ADF roller is located on the left and underside of your lid. The scanning light sits in this area when using the ADF.
You will want to carefully and fully clean the glass in the ADF scanning area. There can also be a strip of transparent plastic on which there can be a mark or smudge. Look for scratches, tiny spots and marks of any sort. You can use a soft lint free cloth either dry, with a little soap and water or water to clean the glass and may have to scrub until it squeaks to remove certain types of marks.
NOTE: Please do not spray the cleaning solution on the glass.
Another way to ensure the mark is removed is to use a credit card by placing in on a angle and sliding it across the glass in one direction. You can then lift the credit card when reaching the end of the glass and return to the other side to slide it across again.
After cleaning the platen glass, run four to five blank/clean pages through to test it.
