Q: What part is needed to turn the reduced engine power light off permanently in a 2007 Buick LaCrosse

The check engine light indicates that there is likely something wrong with the engine or transmission in your vehicle and will usually come on in conjunction with the vehicle going into the reduced power mode. This happens when the vehicle computer detects something wrong with the engine or transmission that may potentially cause further damage or present a safety issue. It is important to have this diagnosed as soon as possible as it could range from something minor to something more serious. Unfortunately, there are many different reasons for this light to come on and the best way to diagnose is to have the vehicle hooked up to a scanner which will download the engine fault codes indicating more specifically what may be wrong. If the fluid under the vehicle is transmission fluid and is leaking, this may explain the reason for the reduced power mode. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.