HP 815MFP - Manual (Page 54)

48 hp designjet 815mfp & scanner 4200
the problem is the wait and diagnostics lights are
flashing
Simultaneous flashing by both the “Diagnostic” and the “Wait
(Warm-up)” lights may mean that that the scanning area needs
cleaning.
1. For cleaning instructions see maintenance procedures on
page 24.
2. Restart the scanner after cleaning.
If the Diagnostic and the Wait lights continue to flash after cleaning
and restarting, then there may be camera position errors. See tell
me about hp customer care on page 90.