HELP Yukon Service Engine light

Hey! I have a 2000 Yukon with the check engine light on. Here's what's odd... I just had it inspected and had no problems I took it back to the inspection place and they said there were no codes and
that everything appeared correct. Then the light went off. After a week of the light functioning EXACTLY as it should, it has come back on. Does anyone have any idea what could be causing this? Is it a short? No codes means nothing can be identified as a problem. Thanks
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