HP Color LaserJet Enterprise MFP M681
Troubleshooting. Engine diagnostics
The printer contains extensive internal engine diagnostics that help in troubleshooting print quality, paper path, noise, assembly, and timing issues.
Engine test button
To verify that the printer engine is functioning, print an engine test page. Use a small pointed object to depress the test-page switch located on the rear of the printer. The test page should have a series of lines that are parallel to the short end of the page. The test page can use only Tray 2 as the paper source, so make sure that paper is loaded in Tray 2.