Thanks for all response.

First of all, I am in Korea not USA.

>I have no details on the emission test specifications,
>but to get an approval for an engine / car model
>combination you have to pass a test with a duration of
>about three days. For a renewal of the certificate
>(every two years) it does not need more than a CO
>reading according to the manufacturer definition.
That's what I mean, tolerance limit of each pollutant like CO, NOx, HC etc.
So far as I know, they should have the regulation on that,
even not allow for owner to know.
At least with the limits, I can compare with my country's regulation.
German Transport Bureau's website where the regulation is would be much
helpful.
If anyone has any clue, I will appreciate.

Thank you.
Chibong

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