Press and hold the button (red triangle), then press and hold the Power button.
: Canon does not officially distribute this tool to the public; it is intended for authorized service centers. Most "Top Download" links found online are hosted on third-party file-sharing sites. Malware Risk canon service tool v3900 download top
Releasing all buttons; the power light should remain steady green. Security and Compatibility Warning Official Sources Press and hold the button (red triangle), then
: Using the wrong version of the Service Tool or failing to enter Service Mode correctly can "brick" the printer's logic board, rendering it permanently unusable. rendering it permanently unusable.