I purchased the unit from a private party and the original owners manual was not available. Having the ability to download it was extremely helpful and clarified operating the equipment immensely. This is a complicated unit and without the manual I would not have been able to maximize it's potential. Thank you.
Text excerpt from page 14 (click to view)
Basic Operations of remote
Accessory of the KDC-4023
Loading and Replacing the battery
Use one lithium battery (CR2025). Insert the batteries with the + and â poles aligned properly, following the illustration inside the case.
In Tuner source
[FM]/ [AM] buttons Select the band. Each time the [FM] button is pressed it switches between the FM1, FM2, and FM3 bands. / [Â¢] buttons Tune up or down band. [#0] â [#9] buttons Press buttons [#1] â [#6] to recall preset stations.
Store unused batteries out of the reach of children. Contact a doctor immediately if the battery is accidentally swallowed. Do not set the remote on hot places such as above the dashboard.
In Disc source
/ [Â¢] buttons Doing track forward and backward. [DISC+]/ [DISC-] buttons Doing album forward and backward.  button Each time the button is pressed the song pauses and plays. [#0] â [#9] buttons When in <Direct Track Search> (page 13) and <Direct Album Search> (page 12), enter the track/disc number.
[VOL.] buttons Adjusting the volume. [SRC] button Each time the button is pressed the source switches. For the source switching order refer to <Selecting the Source> (page 6). [ATT] button Turning the volume down quickly. When it is pressed again it returns to the previous level.