why is one head light dim and the other normal

The check engine light you are describing is not related to your headlight issue. Headlights don't just burn out -- they also get dimmer over time. You most likely just need two new headlight bulbs -- replace them in pairs since if one is going bad, the other is likely not far behind. The Check Engine light will be a different issue.

i just had the same problem i went to walmart bought a cheap wire tester and took out both head lights my dim light was on the right side so i turn the head lights and poke the tester throuth the wires and what i got was on the oranage wire was a real faint light but on the other wires i got bright so i followed the oranage wire and found it was broken or allmost another thing too is try with the key off and then with the key on and same with lights and you will find the wire mine was in the front on the left side down close to the water jug on a 2000 sunfire email me if you want not to good at explain things buckortwo@hotmail.com

the wiring harness in a lot of GM cars ,,are JUNK