Engine light stayed on, Hummer was not starting all the time sometimes had to wait a long time, then it would start. And would idle a little rough. I first replaced the Camshaft Position Sensor- Intake side and still had the same problem. Then I replaced the Camshaft Position Sensor- Exhaust side, FINALLY, engine light went out and starts right up! Been driving for 2 days, still no problems! (hope I'm not being confident to soon, lol)

 

Had same issues on an 2009 I5 H3t it was the cat. Replaced it light went out and truck runs.......PS I did not have a cat code