Mitsubishi MOTORS Outlander PHEV 2018 Owner's Manual page 275

Indicator light, warning light, and information screen display list
Screen
5
5-154 Features and controls
Cause
 EV priority mode is not available because the main
drive lithium-ion battery level is low.
 EV priority mode is not available because the cruise
control or the Adaptive Cruise Control System
(ACC) is operating.
 EV priority mode is not available because the EV
priority mode is limited to protect the Plug-in Hybrid
EV System or outside temperature is too cold.
 EV priority mode is canceled because the main drive
lithium-ion battery level is low.
 EV priority mode is canceled because the vehicle
speed of the cruise control or the Adaptive Cruise
Control System (ACC) is set.
 EV priority mode is canceled because the protecting
device of the Plug-in Hybrid EV System is operated.
Do this (Reference)
Refer to "EV switch" on page 5-62.