OK, here goes: -
Key on, let the dash panel do its self-test. All gauges sweep full scale, all warning lights flash, all digital icons (incl. SERV CODE) in display window appear, & warning buzzer sounds.
Check the top RH corner of the digital display window indicated by the red rectangle in the illustration above. After the self-test completes does the SERV CODE icon remain illuminated or not.?
If it is blank, there are no Active Diagnostic Codes.
If it is illuminated there is at least one Active Diagnostic Code.
The switch to the right of the panel (circled red) can be used to scroll through the various different modes of the digital display window. One such mode is the Diagnostic Mode where you can see the Codes. Press the switch once and then release to scroll from one mode to the next, repeat as many times as necessary.
In Diagnostic Mode each Code will appear in sequence one after the other. Each Code appears in a 2-step process.
First step will show the Module that registered the Code (e.g. 030 or 113)
Second step will show the component and the Failure mode. (e.g. 096F03, 248F01)
Write down each Diagnostic Code in the list and note carefully for each one whether the SERV CODE icon appears or not.
The end of the list usually appears as "END" or as three horizontal dashes "---" in the window.
If it is blank, the Code is Logged, meaning it was there once but is not there now. Logged Codes can be erased.
If it appears, the particular Code is Active. Active Codes cannot be erased until they have first been repaired. Repairing an Active Code turns it into a Logged Code.
To erase Logged Codes you will need to somehow acquire (or build, or use a couple of bits of bent wire - you choose) a Click Box, otherwise known as the 4C-8195 Service Tool. Try this thread as some homework.
https://www.heavyequipmentforums.com/threads/the-famous-cat-click-box.72956/
