my van failed nj inspection for emissions and check engine light. on 2007 Chevrolet Uplander

A mechanic replaced cat converter, oxygen sensor and I replaced the gas cap. Still the engine light comes back on.

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3 answers
Get the code read and post on here to assist you. Autozone does this for free.
when was the last time you changed plugs and wires they do last longer than in the old days but not forever
what are the codes you have?