Yes, the pushbutton unit will tell you the high-side pressure, but it's a pain to go look inside the car to see what it is while charging. It's great while you're driving, though, if you want to know that everything is working as it should. (Note that this is current sensor readout mode, not diagnostic mode.)

With the key in position 2 (engine off or running), hold REST for >5 seconds. Once "1" shows up in the left side of the display, press the left AUTO button until the left side of the display reads "7." The right then shows the high-side pressure.

Momentarily pressing REST again (or turning the key to position 0) reverts to normal operation.