from the gcode wiki:
M106: Fan On
Pnnn Fan number (optional, defaults to 0)
Snnn Fan speed (0 to 255 or 0.0 to 1.0))
Your Macro turn the fan to a very low PWM duty cycle ( M106 P0 S1; Power On Fan )
Notice S1, that will be 1 in the 0 to 255 range, you need a 1.0 to use the 0.0 to 1.0 range.
M106 P0 S1.0
M106 P0 S255
for full speed.
Your multimeter probably reports peak volt, you can verify with a little capacitor in series with your probe to even out the pwm signal, if you do not have a oscilloscope. (with S1 you probably get a low volt value with the capacitor in series).