For HU model number CE617U1:
"To turn loudness on or off:
With the unit ON, press and hold 1, 6, and TUNE (right knob.) The display shows LOUD OFF or LOUD ON.
To disable fixed EQ:
With the unit OFF, press one of these combinations of buttons:
1 + 2 + TUNE for SEDAN
1 + 3 + TUNE for WAGON
1 + 4 + TUNE for THROUGH MODE"