How To Fix Printer Error 12 : Printer Open / No EP Cartridge

HP printers and others have a lot of little basic bugs, but if you know how to deal with some of the more habitual problems you will make the printer your friendly companion to your tasks and projects.
Error code 12 Problem: " Open or No EP Cartridge " error message.

Possible Causes and Solutions:
1. Paper path door (IIP/IIIP) or top cover open. On the IIP/IIIP this can be caused by a defective toner cartridge, defective cooling fan, PS4 or PS5 sensors. Also caused by the density adjusting PCA located behind the density adjusting slide switch. This board takes the input from the two sensors and provides info to the DC controller. If the board becomes defective, you will receive an error 12. Easily replaced after removing the top cover and three wiring harness connectors. If you want to attempt board level repair try the electrolytic capacitor, C207 1 uF 6 VDC. On the 4P/5P printers, the top cover is open or no toner cartridge is installed. This error can also be caused by a defective interlock switch assembly.
2. On the LaserJet 4/4+ an error 12 can indicate the top cover open or a broken tab on the cover assembly. On rare occasions a defective paper control assembly or actuator can cause this problem. Verify the tab on the cover is not broken.

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