formulajunky

Ses light, came on tonight after playing with the nos alittle bit, After about twenty minutes on my way home The ses light came on, Only one time before it was the back two O'2 sensers, i was told I didn't need em so i didn't change em, I Had the codes cleared could they of came back? Or maybe the other o2's could of went, Any way of telling Which out a computer to check em cuase I don't have one or know anyone with one, Thanks for any imput guys