HP error 79 service error (formatter firmware failure)
Error 79 (shown as '79 Service Error' or '79.xxxx Turn off then on') is a fault in the printer's formatter, the board that runs the printer's operating firmware. It can be caused by bad data in a print job, a corrupted firmware image, a defective add-on module or a failing formatter board. On LaserJet Pro models it frequently appears during or just after a job sent from a computer.
What causes it
- A corrupt or unusual print job, often a PDF with embedded fonts or a very large image
- Outdated or buggy firmware
- A driver sending data the firmware does not expect, such as a wrong PCL/PS driver
- Faulty memory DIMM, font DIMM or Jetdirect card
- Hardware failure of the formatter board
How to fix it, in order
Work down the list and stop when the printer recovers. The steps are ordered from most likely and least invasive to last resort.
Power off, unplug, and wait
Turn the printer off, disconnect the power cord for 30 seconds and reconnect. If the error appears again before any job is sent, skip to the firmware and hardware steps.
Stop the offending job
Before the printer reconnects, clear the print queue on the computer so the same job does not resend. Cancel jobs in Windows Devices and Printers or macOS print queue, and on the printer if a job is shown.
Test with a configuration page
Print a configuration or demo page from the printer's own menu. If this prints, the engine and formatter are basically healthy and the problem is with the data being sent.
Update the firmware
Install the latest firmware from HP via the embedded web server or HP's firmware update utility over USB. HP has fixed 79 errors in firmware for the M401, M404 and M426 families, so this is the single most effective step.
Change the driver
Switch from the PostScript driver to PCL 6, or install the model-specific driver instead of the universal driver. Avoid printing from Windows Photo Viewer or older applications that generate non-standard spool data.
Print the problem file differently
If one document triggers the error, open it in a different viewer, use Print as Image in Acrobat, or re-save it with fonts embedded differently.
Remove accessories and test
Unplug the printer, remove any memory DIMMs, font modules or network cards that were added, and test. If the error stops, the accessory is faulty.
Stopping it happening again
When it is not worth fixing yourself
If you would rather not work through this alone, a printer specialist can take a look with you on a screen-share and tell you honestly whether the machine is worth saving.
Frequently asked questions
Is 79 service error the same as 49 service error?
They are related. 49 is a firmware exception in the printer's processing code, while 79 is a formatter hardware or firmware fault. Both are handled by clearing jobs, updating firmware and checking drivers.
Why does my LaserJet Pro M404 show 79 only when printing from one PC?
That PC's driver or a specific application is sending data the firmware chokes on. Reinstall the HP PCL 6 driver on that computer and clear its queue.
Does a 79 error go away on its own?
It clears after a power cycle but will return if the cause remains. Treat it as a prompt to update firmware and check drivers.
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