Ahhh, the voice says to check Lambda 1st?

OK then... MY chevy of the day came up with a 15/25 fail in HC and NOx, but CO passing.

The numbers were CO .11, CO2 12.4, HC 204. NOx 1461, O2 3.1(has Airpump). Lambda was a hugely appropriate 1.1555, or AF ratio ... Login to read more.