The door cards are stupid easy to remove. You need a philips or torx screw (depending on the car) driver, a vinyl pry tool, and a 8? 10?mm socket wrench.
Once you have the speaker out and exposed. Use a multimeter with the stereo on, and check to see if you're getting voltage to the speaker.
As for the tweeter: the A-Pillar panel just pulls off from snap clips. Pull out and toward you (the trunk of the car) since the plastic is recessed slightly into the dash where it meets the glass. Careful not to continue ripping outwards, once it unclips ensure nothing else is snagged and then just carefully set it onto the dash. Tweeter will be exposed, check voltages again.
If you're not getting voltages to either speaker/tweeter. Mark down the color code of the wires. Then check the voltages of those wires at the HU. If you get no voltage at the speakers but it registers at the HU then the wiring to the speakers is bad. Cut the existing wires and run new ones to the speakers.
Also another thing I've noticed specific to my car is that the actual harness that plugs into the speakers, (its a plastic adapter), the solder inside starts to erode and the connection goes bad. Best way to test it would be to remove one of your good speakers, plug it into the bad side and see it produces sound. If not then there's another potential culprit. Honestly, I'd start at the harness adapter, swap in a working speaker to the bad side and see if it works. If the harness is bad, you can either buy a new OEM speaker off of rockauto or do what I did and splice a new pair in directly to the wiring with some solder.
Hopes this helps
