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what could cause a high count in the parts per million with the hydrocarbons and nox? my GS passes at the 25 mph test, but not at the 15. the guy said it's cause i have a weak catalytic converter, but i replaced it two years ago, and the cat shouldn't fail unless something else is causing it to become weak.

any suggestions?

I was ONE point under failing the Hydrocarbons part of the test last week. I passed everything else with flying colors though. Any information on this would be appreciated.