There are at least two modes of operation
1) each extruder is a separate tool. Only one tool is active at any one time. Tools are switched with the T0 or T1 command
2) mixing extruders. Each extruder is given a percentage out of 1 and that much filament comes out of each extruder. see
m165
Both require being setup in firmware and the appropriate gcodes to change tool or set mixing.
Which one are you trying to setup and how have you tested it?
Edited 1 time(s). Last edit at 04/27/2019 12:13AM by Dust.