New Diesel Smog Check Requirements Coming Soon

Starting in July 2023, the Bureau of Automotive Repair (BAR) will roll out new Smog Check requirements for model year 2007 and newer light-duty diesel vehicles. Based on year-over-year data analysis and advances in diesel exhaust systems, the On-Board Diagnostic (OBD) readiness monitor standards will be updated to further reduce diesel emissions and meet clean air goals.

Since 2010, model year 1998 and newer light-duty diesel vehicles with a gross vehicle weight rating of less than 14,001 pounds have been included in the Smog Check Program. For these vehicles, the Smog Check inspection requires an assessment of the OBD II system to verify that the required readiness monitors have been run and are set. Readiness monitors are vehicle self-test routines used to determine proper functioning of the emissions control system. To pass the Smog Check inspection, model year 1998 to 2006 vehicles must have all readiness monitors set. Because of the complex exhaust after-treatments that were added in 2007, model year 2007 and newer vehicles have been allowed to have up to two unset readiness monitors to pass a Smog Check inspection. Starting in July 2023, the readiness standards for 2007 and newer light-duty diesel vehicles will only allow the Diesel Particulate Filter and the Non-Methane Hydrocarbon Catalyst readiness monitors to be unset.

A small number of vehicles have been found to have design-related issues that may prevent them from meeting the new monitor readiness standards. These vehicles will be exempted while the manufacturers correct the design issues. During the Smog Check inspection, the BAR On-Board Diagnostic Inspection System will automatically identify these vehicles and exempt them without requiring input from the Smog Check inspector.

For a summary of readiness standards for the OBD test portion of a Smog Check inspection and a list of the exempted vehicles, refer to the On-Board Diagnostic Test Reference webpage at

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