I don't know how different 2004 is from 2012... but the 2012 manual talks about being able to find the engine error code by pressing the mode button and reading it from the instrument cluster.
1. If the error codes are not displayed, use the
mode button to toggle until “Ck ENG” displays
on the main line of the display.
2. Press and hold the mode button to enter the
diagnostics code menu.
3. Record the three numbers displayed in the gear position, clock and odometer displays.
4. Press and release the mode button to advance to the next error code.
5. Press and hold the mode button to exit the diagnostics code menu.
6. See an authorized VICTORY dealer for code details and diagnosis.