So i took my valve cover off to paint it, and now i noticed that my check engine light is on after i put it back together. The only thing is i dont remeber if it was on or not before i took the valve cover off. Could taking off the valve cover and putting it back together turn on the check engine light if something is not sealed correctly. And last if the check engine light was already on could the fact that i have 155,000 miles on it cause it to be on?