Q: Reduced engine power 2004 Grand Prix

Hello - you don’t specific what code is causing the Check Engine light to illuminate (oxygen sensor problem), but a failure of the pre-catalytic converter O2 sensor could cause a Reduced Power experience. Failure of the O2 sensor can cause the engine to run too rich, passing unburned gas fumes to the catalytic converter, a real overheat/fire damage possibility. I recommend a Reduced Power inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.