2002 Nissan Maxima Engine light

I have a 02 nissan maxima 3.5 v6 and I just got my sparke plugs changed and to get my sprake plug changed they guy had to remove the headers (or something like that) and I he told me to get a new gas kite because you dont want to put the same one back on. So everything was done. The ride of the car is good too. But after like 6 hours later my engine light came on when I start the car. I was wonder if you guys know what wrong with it.