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.

2 answers
a trailblazer has a 4.2 litre engine.whats your question friend?
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.