Check the airbag wiring under the dash. Obvious as hell, it's all yellow. Also, make sure you didn't 'bump' the airbag sensor on the front rad support. If it's in the 'on' position, the ECU will throw a fault code (thank god, or alot of people would have airbags blowing up in their faces when they turn the key).
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2002 Sunfire -->
- Ractive steering wheel
- ASA 17" EM9 + Nexen N5000 215/45/17 (steelies for winter)
- D-Spec Lowering kit @ 1.4" (issues currently

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- Rockford P250.1 + MTX MZS1004 + Panasonic CQ-C8313U head unit
- Barely legal tint.
2 words...
SCAN TOOL!
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Have you had the passenger seat out in the process? If so check the connection to the airbag control module under the passenger seat. When I replaced my dash (had the seats out) my knee rested on this (but I did not realize). I disconnected it and this is what happened (the light came on). If you have acces to a good scan tool that works as well.
FU Tuning