gm diagnostic tools
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.
The system was built because the EPA decided people were not concerned enough with emissions, and if people thought they had an engine problem they would get it fixed, but if they knew it was a simple emissions problem they would let it go.
