If you have a paper jam on an HP OfficeJet Pro X451DN, you will want to check in the duplexer unit as often, that is where it will hide.
Detecting the Jam
01. Turn off the HP OfficeJet Pro X451DN using the power button.
Note: If the power button will not work, pull out the power cord.
02. Leave it unplugged for 60 seconds to cool to prevent skin burns.
03. Carefully open the left side of the HP OfficeJet Pro X451DN.
04. Remove the duplex module at the bottom.
05. Next, lower the blue lever in the middle.
06. Look for any pieces of paper in the parts and printer.
07. Put everything back carefully, except the data cable.
08. Reconnect the power cord and power up the HP OfficeJet Pro X451DN.
09. Try to print a report directly from the printer, not your computer.
Note: If there are curled up paper hidden inside, this will force it out.
10. If it jams again printing the report, leave it on and follow steps 3 to 7.
11. You should now see any pieces of paper and can remove it.
12. Close the printer. The HP OfficeJet Pro X451DN will print your report.
13. Attach your data cable and wait a minute for the print jobs to come out.
14. If nothing comes, try and reset the print spooler.
Warning: When removing the duplex module avoid making direct contact with the black cylinder to prevent ink smear (on the skin, clothes, etc) and keep it level to avoid spilling any maintenance ink. Also, when removing the duplex module, do not let the bottom of the duplex module touch or rest on the ribs on the left door as it can damage them and might lead to paper damage and frequent jams.