My check engine light has been coming on occassionally ( 03 MDX ) I clean the gas cap o-ring and make sure cap is tight and light goes off. Lately, this is not working. Went to Autozone and had them read the codes. They came up with P0420, catalyst system efficiency below threshold B1, and P0455 evap system ( very ) large leak detected. twice.
Is this a major concern?

 

Are you required to pass emissions testing?
Have you noticed that you are adding more oil more often, between oil changes?
Has your gas mpg gone down?
The ecu is being told by the O2 sensors that the expected "values" being read, by the O2 sensors, are incorrect.
Then the ecu makes the air/fuel mix more lean, by adding (up to 20%) more gasoline.
Eventually your catalytic converter will become clogged. One day, when trying to accelerate on to a highway on-ramp, you'll lose power no matter how hard you press the gas pedal.

 

Haven't noticed these symptoms yet. Thanks, will get this taken care of soon as possible. No emission testing here, but I like to stay on top of maintenance.