What causes emission system failure warning light staying on and is it serious? on 2009 Chevrolet Trailblazer

I'm driving a Captiva 3.2 LTZ V6 2009 model, the emission system warning light stays on even when the car is running. Sometimes the light comes off and only to come on later.

Asked by for the 2009 Chevrolet Trailblazer
Need a scan test and it may have to go back to a dealer. Not many Captiva's around, at least not here in the East. Also i guess that is why you could not enter that vehicle on this site. Don''t think it's too serious, since the light goes off at times.
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a trailblazer has a 4.2 litre engine.whats your question friend?