The check engine light is because all check engine light codes are caused by components that affect emissions. It's not actually an engine problem, it's a problem with either your O2 sensor, MAF sensor, fuel/air ratio, pyrometer, or exhaust.you can start with an
OBDII code reader, which you can get for free at your local parts store. This will tell you what component is malfunctioning, and then you can decide if it's worth fixing or not. But rest assured, the oil leak has nothing to do with your check engine light.