Aftermarket Catalytic Converters and California Motorists

Replacement catalytic converters are always a cause for concern, because non-certified aftermarket or used catalytic converters are not only illegal, but they can also emit harmful levels of pollutants. Smog Check technicians know how to look for illegal converters and must fail motorists with improper equipment. Effective January 2009, California required that all aftermarket catalytic converters sold must have proper emissions performance and be compatible with On-Board Diagnostics II (OBD II) equipment. This means that the replacement catalytic converters cannot cause faulty signals on the OBD II, and conversely, the OBD II must be able to generate the correct fault signal if the converter fails. All aftermarket catalytic converters must have full five-year or 50,000 mile warranties.


However, some vehicles were built prior to the implementation of OBD II, so these vehicles are exempt from having aftermarket converters that are compatible with the OBD II system. Instead, these vehicles simply have to be equipped with approved converters that meet certain emissions performance standards in California.


Before 2008, California permitted certain used replacement catalytic converters to be sold, but this is no longer allowed. The Air Resources Board in California decided to outlaw such practices and no longer tolerates certified used catalytic converters because it was impossible to be certain that minimum emissions standards were being met.


California is more stringent than other states, so although a U.S. manufacturer may have an OBD II-compatible catalytic converter for sale, it is not automatically approved for use in California. Installers need to be sure that the catalytic converter they order is truly legal for use in the state of California. The new replacement converter has to be installed in the same place as the original one, and a new converter can only be installed if the original one is truly malfunctioning. Before replacing a catalytic converter, make sure that the warranty has expired for the original one.


Replacement catalytic converters that are legal in California all have an Air Resources Board Executive Order number permanently marked on the outside. The Smog Check technician will make sure that the converter is properly connected and passes the emissions test. Often catalytic converters are susceptible to clogging from some kind of failure within the converter from high temperatures. Motorists may notice that their engine is more sluggish if the converter is clogged, or sometimes a distinct rattling sound can be heard while idling that may indicate that the catalytic converter is clogged or broken.