•HP Laserjet 4250, 4350 Printer Engine Test Button Location

Engine-test page
To verify that the engine (all printer components except the formatter, formatter DIMMs, EIO products, and the stacker or stapler/stacker) is functioning, print an engine-test page. Use a small, non-metallic, pointed object to depress the test-page switch, which is located on the right side of the printer.

The test page should have a series of vertical lines. The test page prints from the last tray that you printed from. However, if the printer has been turned off and then on again since the most recent print job, the page will print from tray 2. The printer will continuously print test pages as long as the test-page switch is depressed. The printer will not print a test page if it is in Power Save or Sleep mode.
NOTE A damaged formatter might interfere with the engine test. If the engine-test page does not print, try removing the formatter and performing the engine test again. If the engine test is then successful, the problem is almost certainly with the formatter, the control panel, or the cable that connects them.