The origin of the problem
I can tell if an Outlander PHEV has a problem with the heating system. It starts to lose heat at about 40-50K miles because the antifreeze coolant starts to crystallise and block the filter in the filter housing. If your vehicle has a PTC heater click here Mitsubishi Outlander PHEV heating problem with PTC heater, filter
High voltage can kill you, so do not remove or dismantle, the orange cable or high voltage component let to do the proper qualified technician.
How to it sort out
The filter is blocked with crap, looks like sand and gale, the same as in the picture.
The filter housing is located on top of the gearbox, just simply remove and separate it in half clean it out and refit the top up with coolant and start the engine it should work. I recommend cleaning the filter every third service and thus we can reduce further damage.
When working, the right way the next day checks the coolant level and coolant strength.
Coolant capacity 6.5 litres.