You cannot access advanced diagnostics without the service manual. The K8600 has a hidden "Service Mode" that is not documented anywhere else.
How to Enter Service Mode (from the manual):
What you can do here:
The Symptom: After moving the printer or replacing a printhead, you get an "Ink System Failure" error.
The Manual’s Solution: The K8600 uses a gravity-fed ink system. Air bubbles are the enemy. The manual contains the official "Priming Procedure," which overrides the normal startup sequence to force a purge cycle. It also details how to reset the Service ID (a hidden timer that tracks printhead usage) via the front panel buttons. hp officejet pro k8600 service manual
Unlike the standard "User Guide" that comes in the box (which teaches you how to load paper and replace ink), the Service Manual is a technical document written for HP Certified Technicians.
Answer the yes/no questions. For example: "Does the paper advance past the registration roller?" If yes, go to step 3. If no, go to step 7. You cannot access advanced diagnostics without the service
If you own an HP K8600, you have likely encountered one of these three infamous errors. Here is how the service manual solves them.
This is the "meat" of the service manual. It provides step-by-step removal procedures for every major component, accompanied by exploded-view diagrams. What you can do here: The Symptom: After