VSC off/VSC trac/check engine light

I've seen several posts with this description, some with an ABS error as well (which I do not have). My brother is a mechanic and seems to think this problem is a bad oxygen sensor. These lights have been coming on and turning off for the past year, and I have had the car for about 2 years. Upon taking my car to AutoZone, I received codes indicating that the issue was emissions-related (I don't remember the codes specifically, sorry). Previously, it didn't seem like there was a pattern to when the lights came on, but after closer examination, it seems like they come on when I'm driving up rough mountain roads, and they come on immediately if I turn on 4wd. I'm not a mechanic, but I'd like try to understand what's going on if someone can share some insight, and some suggestions as to what I should do would be fantastic. Thank you.

 

all Toyota's 99 and up will have the ABS/VSC lights come on when the engine light is illuminated. So you only need to find out why the engine light is coming on.