Well, I went to the Valvoline during lunch to get my oil changed, the rear diff fluid changed, fuel injectors cleaned, engine flush, and a complete fuel treatment. When I left I noticed my check engine light was on. My truck only has 17K miles on it, so I was wondering if anybody had their check engine light turn on due to fuel system treatment being present in the fuel? Or maybe it's just something stupid like the oil cap isn't tight. I'll have to swing by there after work I guess. What are your thoughts?