Dell P1500 Personal Mono Laser Printer - Manual (Page 62)

The printer is in the Ready mode, Hex Trace is active, and the toner in the
toner cartridge is getting low.
What you can do:
Advanced users can use Hex Trace to help troubleshoot printing
problems. After resolving the problem, turn off the printer to exit Hex
Trace.
Remove the toner cartridge and gently shake it to extend the life of
the cartridge.
Replace the toner cartridge .
What this light sequence means:
The current print job is canceled.
The printer is resetting to the user default settings. Any active print
jobs are canceled. A user default setting remains in effect until you
change it or until you restore the factory default settings.
What you can do:
Wait for the message to clear.
What this light sequence means:
The printer has a service error and printing has stopped.