These service codes mean that there is an issue with the paper tray.
501 = tray one, 502 = tray two, 503 = tray three, 504 = tray four
To fix these codes, please follow the steps listed below:
1. Open the bypass try on the right side like you are removing a jam.
2. Take paper out of whichever tray is listing the problem (see above in red).
3. Turn off machine completely by the switch under the clear plastic flap.
4. Leave machine off for a few minutes.
5. Turn machine back on by switch.
6. Machine should than say the tray is empty.
7. Fill the tray with paper only to the fill line, DO NOT GO ABOVE FILL LINE!
8. Everything should be fixed!
If for some reason these steps do not fix the issues you're experiencing, please request service.