i recently bought a used Focus and today one of the headlights (low beam only, high beam works) went out. I changed it and it still didn't work so I went to check the fuses in the box next to the engine. One of them was blown so I figured that was the one for the dead light. And then I swapped the fuse with the one that looks exactly the same under it, and it worked! i then drove to the shop to buy new fuses without swapping it back. On my way to the shop, the check engine light came on. I thought nothing of it and figured that it would turn off once i replaced the fuse. but it didnt turn back off. so heres my question.could it be possible that the light came on because i pulled out that other fuse? if so then will it turn back off later on? i dont think that its a coincidence that i pulled a fuse and something is wrong with my engine. but i want to be sure because i dont have money to fix it. i searched the ford manual and the fuse i pulled might have been the o2 sensor?