So i’ve got a sierra that was a hand me down from my big brother who bought it off of some guy in our town. i’m just now learning how to do basic stuff with vehicles. everything has been going relatively good with it, it needs a rear axle seal replacement, new tire, oil change, and that’s about all i can tell. it’s giving me a check engine light how do i go about seeing what’s wrong? he told me that the engine was replaced entirely but he’s not sure about any details, how can i figure out what’s been put in it?