Won't use tray 2 when tray 1 is empty

Have you tried checking that tray 2 has the same paper type as tray 1. If your machine is network attached, you can access the embedded web server (where device settings can be adjusted) by entering the device IP address into a browser. Find the web address from the machine by going to menu (key icon), reports, then arrow over to network set up page. NSP is a 1 page report which will tell you the IP address. Go to a web browser and type in that IP address. Should take you to your device web page. From that page you can change the device settings (click on settings and then paper menu). Check to be sure that the same paper type is set for both tray 1 and tray 2 (and be sure that tray 2 is showing up on the list). I had to power the printer back on for it to recognize tray 2. Hope it helps