bbvc

I am looking to buy a used Lancer GT 2012 but I see many of them has the yellow triangle exclamation light on the dash, what does that actually mean?
I read a few posts, they were mentioned that anything you change on the car will caused that light on and some said that's the problem with the timing chain in the engine or engine problem? should I go for it? is it easy to fix?
Or should I buy a brand new one? But will that light come on easily?
Thx!