Its a boush o2 sensor and yes the check engine light comes on when I go to acclerate the car. Could bad gas be a issue as well. Cause the gas has been in the car for a while would that be the cause for the o2 sensor to send a code as well. That the gas isnt any good and the car isn't able to burn it right. Just some thought I really dont know. Thats the only thing I could think of what coud cause the problem.