Found a function on the MXT400 the other day that I didn't see in the manual. You can scan for CTCSS or DCS on a channel if you long hold the CTCSS/DCS button. The codes will start scrolling. If there are active communications on that channel, it will eventually pause on the code. I've use it on the repeater channels to help figure out repeater tones if there's chatter.
How long do you have to hold it? Doesn’t seem to be doing it on mine.