Hey everyone. Today I noticed that my passenger side headlight was out. I turned the switch to just have my running lights on and to my surprise my passenger running light come on but my driver's side running light stayed off. So I tried my highbeams. When I turn those on only the driver's side comes on.

What is causing this?

Sounds like you finally finding them buren out bulbs you never looked for..

Go buy a new bulb for each lamp that does not illuminate when light switch on.

Dont forget the rear too.... have assistant step on the brake pedal while you watch to make sure you have 3 lights illuminate brightly when pedal pushed

Sonata has :

Left front and right front side mark lamp at at the bumper cover (orange w/194 bulb)

Left & right low beam

Left & right high beam

Left & right front turn signal bulb

Left & right rear side mark bulb (little section of lamp at leading edge of lamp assembly

Left & right rear tail light (4 of them,, 2 will get brighter when step on brake pedal)

Middle (3rd) brake light in rear window, some is bulb, some have LED strip
left & right license plate bulbs

Left & right fog bulbs if applicable