Ok so you know the interior trim panel at the far back of the car. If you have a rear wiper, you will have a washer fluid tank filler there.

My car has no rear wiper or front headlight washer. So there shouldnt be a tank there I think. But there is a hole for the filler cap!

Im trying to figure out if this is the wrong rear interior trim piece or if there is some kind of hole cover that's missing.

thanks!

 

Yes. I believe all rear plastic panels were the same regardless of equipment packages. There should be a simple round plastic plug or cover that snaps over that hole. Apparently your's is missing. It comes off pretty easy, I used a bit of clear silicone to secure mine a little better. If you haven't already, you might want to pull the carpet back and look closely down in the spare tire well.