Though there are many reasons for poor quality or lines on your MFP's output, one that we often find, and that is end-user resolvable is associated with a soiled scan glass.

*MFP - Multifunction Product/Printer/Peripheral
  MFD - Multifunction Device

Output has a line running from lead edge to the trail edge (as exiting the device) while using the document feeder:

 A good way to see if the line is coming from a soiled scan glass would be: Place an original manually on the glass without using the document feeder and make a copy. If the line is no longer there, the problem likely will be that the scan glass is dirty. The scan glass can be found by lifting the document feeder. It will usually be about an inch wide and 12 inches long running from front to back,  located to the left of the manual copy glass. Often times looking at the scan glass, it may appear clean, when there is actually a small amount of pen ink, white out, glue, etc. that has transferred itself from an original.  A vigorous cleaning of the scan glass with glass cleaner, alcohol or some other preferred cleaning solvent  should give you a crisp, clean output again.