CEL came on. by the descrip of the list of probable causes, it seems like it leads to the 02 sensor up front? i've noticed a decline in my MPG's since the light came on as well. 4c 2.2l 125k miles. the drop in MPG's is probably in part of the sub zero temps that we've had in IA for what seems like forever now. the car starts fine and isn't rough when driving or idling. i'll probably run some Seafoam though the gas tank. guy I work with is changing my o2 sensor for me this weekend. Assuming i'm right here (please tell me if i'm wrong about the 02 sensor), which sensor do you guys recommend getting? I've got advanced auto and o'rileys local.