Operation CHARM: Car repair manuals for everyone.
Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

(Some people have issue connecting. LEMON is investigating. For now, use Firefox or change your DNS server)

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Emission Control Systems: Description and Operation



Emissions Classifications







The illustration shows the relationship between the different emissions classifications.
- Tier 1 (the applicable obligatory requirements, both federal and in California)
- TLEV (Transitional Low Emission Vehicle)
- LEV (Low Emission Vehicle)
- ULEV (Ultra Low Emission Vehicle)
- LEV II (Low Emission Vehicle, stage 2)
- ULEV II (Ultra Low Emission Vehicle, stage 2)
- SULEV (Super Ultra Low Emission Vehicle)
- NOx g/mile (nitrous oxides)
- CO g/mile (carbon monoxide)
- NMOG g/mile (Non-Methane Organic Gases). These are the basis of smog. In principle NMOG are hydro-carbons
- "A"symbolizes the optimal target of the car when it leaves the factory.