Sharp AL-1540CS Single By-Pass works, regular copying get flashin

Could be dirty feed rollers. I am assuming you are selecting the lower tray as your paper source when you get the "P"
OK, so take out the paper tray. Remove all the paper and look for 2 felt pads on the metal spring loaded plate where the paper sits. Spray these 2 pads with glass cleaner. Wipe of the excess spray from the metal plate. Install the tray, select that tray as your paper source and hit the print button. You will get the "P" of course so just hit C then print again. Do this several times. What you are doing is having the feed rollers rotate against the pads and thus cleaning them. After you do this 5 to 10 times then remove the tray. Dab a dry cloth on the pads to dry them somewhat, add paper and re-install the tray. If the problem was dirty feed rollers then this will fix it. The other cause of your feed trouble could be a paper feed clutch going bad. This was somewhat of a common problem on these machines. You would need a service tech to get to the clutch, remove, clean, lube and re-install it. But only if the above procedure does not work.