Firmware error B0605 on HP LaserJet P2055dn
A common error message on the HP LaserJet P2055dn series is the B0605 Firmware Error. This error basically means the printer's firmware (controlling software) has crashed.
If you are handy with a computer, the first step is to follow HP's trouble-shooting steps and re-flash the firmware in BootCode mode, then reboot the printer. Re-flashing the firmware doesn't always help, but it's a good first step. See HP's trouble-shooting document here: Error B0601, B0602, B0603, B0604, or B0605 displayed during printer initialization
If this process does NOT fix your B0605 firmware error, you will probably need to replace the formatter assembly, which is the main logic board in the printer.