Left side speakers are Not working properly??

the easiest way to check would be to remove 1 speaker from the left side and plug it in on the right side.

Is it an Infinity Sound System? Great system in my Chrysler Van but I had a similar problem. Check the balance system and check if front or rear speakers are operating. I spent many hours of taking apart panels (glove compartment, front kick panels) only to find that there is no single amp but each front door has a built in amp bolted on each speaker! Be careful looking at YouTube as a lot of wrong info. Found out that water dripped down the window and shorted the amp. Is the small speaker in the top of the dash work? Difficult but possible is the wire going from the frame thru to the door broke due to constant flexing opening and closing.