Printer with two extruders but one as a backup
You could use a &quot;filament runout sensor&quot; and combine it with a &quot;filament running sensor&quot;. If either fails the controller needs to be notified by a signal. If you configure the Configuration.h filament runout setup such that it doesn't call M600 but instead a series of codes to park tool 0, activate tool 1, home tool 1, prime tool 1, and commence printing, you are near a solution.