On my 2016 Prius 2, the EV indicator in the HSI never appears, even when the car is clearly operating on the motor alone, or when “EV mode” is selected. Why is this? I can see the space in the HSI curve where the indicator should appear, but no indicator.
Are you the original owner? There is a setting to turn it off so the previous owner might have done so.
My EV indicator has never been totally accurate when driving HV. I've never tried to use EV mode (from the button). I gave up trying to use that display for any useful information. If I want to know if the ICE is OFF (i.e., using EV) I will switch to the power distribution screen and it does a better job of showing whether the ICE is providing drive power or not. I'm generally in the fuel economy history display that shows the recent four days of miles/MPG, and don't really care about HV/EV operation anyway.
Wait, I think I found it. In “meter customize” menu. Who would have thought you’d want to turn this on and off?