Only one side of the speakers work passenger side

Hi have you tried using the settings on the stereo that controls the balance from front to back and side to side if you have changed these settings without knowing then the stereo output might be in the possition for the one side.
If after doing this you still have the same problem then i would remove the stereo and check all the wires are secure if they are then you need to remove the casing for the side speakers and check the wires for corrosion and make sure connected properly.

Usually the speakers wont just suddenly stop working if the problem was with the speaker then you would have noticed over time that the sound was distorted or would have sounded crackley from the speakers.
If this is not the case then check the speaker balance on stereo and then check wires.

Let me know how you get on or if you need further assistance ok

Have a radio tech check it out sounds as if it has blowen one side