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Diesel Smog Inspection

Diesel Inspection Procedures

What is the diesel Smog Check inspection procedure?

The diesel Smog Check inspection will consist of three parts; a visual check of the emission control equipment, a check of the OBD system and a test for visible smoke.

All of these tests are currently performed on gasoline vehicles. However, there are some differences as indicated below:

  • The visual check of diesel vehicles will be performed the same way as the test performed on gasoline powered vehicles except that the emission control components maybe different. The instructions for performing the visual inspection can be found in the Smog Check Inspection Procedures Manual.

  • The OBD-II check on diesels will be conducted the same way it is performed on gasoline vehicles. The BAR-97 cannot perform the OBDII check for any vehicles with the newer Controller Area Network (CAN) OBD communication protocol. Some diesel vehicles started using the CAN protocol as early as the 2003 model-year.

  • The visible smoke test procedures for diesels is similar to the gasoline procedure. The procedure can be found in the Smog Check Inspection Procedures Manual.

Will diesels be required to have an ASM or TSI test?

No, dynamometer testing will not be part of the diesel Smog Check inspection.

Will Smog Check technicians be required to check for alternative fuels?

No. Although some diesel vehicles owners use alternative diesel fuels, including various mixes of biodiesel, currently, there are no plans to require technicians to collect fuel samples as part of the diesel Smog Check inspection. If a vehicle has equipment that modifies the fuel injection system, then the system must have an ARB approved Executive Order (EO). Extra fuel tanks without evaporative controls are not a cause for a Smog Check failure.

How long will the diesel Smog Check inspection take?

Although many factors affect the length of time it takes to do any type of inspection, the BAR expects most technicians to be able to complete the diesel inspection in approximately 15 minutes.

Implementation Schedule and Other Miscellaneous Questions

When will diesel inspections begin?

The DMV will begin mailing notices to motorists who own diesel-powered vehicles subject to the program for registrations due in April 2010. However, change of ownership and out-of-state inspections will be required starting on January 1, 2010. Unlike gasoline-powered vehicles, there is no six-year or four-year exemptions on diesels included in the Smog Check Program.

Why was 1998 established as the minimum model-year vehicle subject to the program?

The law, as written, authorizing the inclusion of diesel vehicles into the Smog Check Program, required it.

Will any diesel vehicles be exempt from the program?

Yes, all diesel vehicles over the maximum 14,000 Gross Vehicle Weight Rating (GWVR) limit will be exempt from the Smog Check Program. The GWVR is indicated on a label located on the chassis or door jamb of the vehicle.

What other states smog check programs are inspecting diesel vehicles?

Diesel vehicle inspection programs are operated in Nevada, New York, and Colorado.

Repairs and Subletting

How does the BAR expect failed vehicles to be repaired?

Currently, most diesel vehicle owners have their vehicles repaired at either a dealership or a diesel specialty repair shop.

Will subletting be allowed?

The “Smog Inspection Requirements” regulation package allows for subletting of diesel vehicles with Smog Check related repairs. The same rules for the subletting of catalytic converter repairs will also apply to diesel vehicles.

Test-Onlv Direction

Will BAR be directing diesel vehicles to Test-Only stations?

No, the BAR will not be directing diesel vehicles to Test-Only or Gold Shield stations for the first few years of the program.

Tampering, Engine Changes

Will Smog Check technicians be expected to identify modified or tampered emission control systems?

Yes, ARB indicates that diesel vehicles subject to this program have been certified to meet strict emission control requirements by the United States Environmental Protection Agency (USEPA) and the ARB. As a result, Smog Check technicians will be required to fail vehicles with modified emission control equipment or devices that have not been approved by the ARB. Often approved devices will have a label with a ARB Executive Order (EO) number on it.

Can BAR provide a web-based database available to help technicians identify which equipment is illegal?

Information about aftermarket equipment devices that are approved by the ARB is already available on their website under “Aftermarket Parts”. You can search either by the device description or by the Executive Order (EO) number assigned to the device.


Green StationThe Bureau of Automotive Repair (BAR) has cultivated a partnership with the Department of Toxic Substances Control (DTSC), the agency that regulates the use and recycling of hazardous waste products. This new partnership has given us the opportunity to promote DTSC's voluntary program by which auto repair facilities may become recognized as a "Green Station" if a station meets the DTSC's requirements.
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