ERROR UF-

Question

Copier displaying error code: UF. What does it mean and how to resolve or clear it? The copier can initialize when I turn on the popwer but cannot copy due to error. I carried out simulation 02 and I was able to print several copies but when I lleave simulation. UF displays again. I'd checked the developer powder and found out that it's running out. Does it have something to do with the error? I'll appreciate any help or assistance you will extend to me. Thank you so much.