Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, have you tried checking that everything is in place? ...access door? exercise this door by opening/closing positively (as if about to change the ink cartridges) a couple of times?
Yes thank you for allowing me time to read your posts and compose my reply.
Error 3501 is "access door open" If it has been checked and ensured to be correctly close, then the described symptom would point to an internal hardware issue or more particularly, a failed door access close sensor.
If comfortably able and feel safe to do so, are you then considering a DIY (do-it-yourself) repair approach?
The only easy user doable attempt is to inspect the hinged junction point of the access door and the bed. With a strong flashlight check for any warping of the plastics, out-of-position, or even foreign matter such as bits of paper that may prevent the access door from latching fully/correctly down.
Have you tried this please?
And thank you too for your kind understanding. Unfortunately, there is no quick-n-easy fix and neither is there a workaround; sorry for having to be the bearer of bad news.