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CA Diesel Emissions Testing

CA Diesel Testing Procedures & Regulations






Effective January 1st, 2010, light duty diesel vehicles model year 1998 and newer are required to undergo diesel emissions inspections - in other words, you have to "SMOG" your diesel in CA. Similar inspections are also required in Nevada, New York, & Colorado, while other forms of inspection are required in additional states as well. Light duty diesels are classified as a diesel powered vehicle with a gross vehicle weight rating (GVWR) below 14,000 lbs. Vehicles with a GVWR above 14,000 lbs are exempt from the testing requirements. In this 3 step emissions inspection, the procedures are:

1. Visual inspection of the engine's emissions control equipment.
2. An OBDII (onboard diagnostics system) check.
3. A visible smoke test from the tailpipe and crankcase.


CA Diesel Smoke Test Procedures, as outlined by the California Bureau of Automotive Repair

1. Idle Smoke Test - The tailpipe emissions are observed with the vehicle idling for 10 seconds.
2. Crankcase Smoke Test -The crankcase is observed for smoke for 10 seconds at idle.
3. BAR Snap Test - The engine will be quickly accelerated between 2,000 - 3,000 rpm. Using the side mirror(s), a technician will watch for excessive exhaust soot. The throttle will be snapped 3 times, with 3 second pauses between snaps. The first snap does not count towards the test, meaning any visible smoke that is emitted on the 1st snap will not conclude in a failure of the test. Any smoke plume that appears 5-15 feet from the tailpipe and lingers for more than 3 seconds on the 2nd or 3rd snap will result in a failure of the test.


Visual Inspection

During the visual inspection, technicians will be looking to ensure that all factory emissions equipment is in tact. This includes, but is not limited to, positive crankcase ventilation (PCV), crankcase depression regulator (CDR), catalytic converters, diesel oxidation catalysts (DOC), diesel particulate filters (DPF), selective catalytic reduction (SCR), and exhaust gas recirculation (EGR) systems. They will also be looking for aftermarket components such as exhaust systems, air intakes, etc.


Modifications that DO NOT require a CARB Executive Order

• Air horns (intake elbows).
• Modifications to air cleaner assemblies (cold air intakes, aftermarket filters).
• Exhaust system modifications made AFTER the last emissions control device.
• Auxiliary/aftermarket fuel filters or fuel-water separators.
• Aftermarket lift pumps & auxiliary fuel tanks.
• Water injection systems.


Modifications that DO require a CARB Executive Order

• Turbocharger modifications or aftermarket turbos.
• Aftermarket intercoolers.
• Modified or aftermarket injectors or injection pump(s).
• Propane, methanol, hydrogen, or nitrous oxide injection.
• Aftermarket exhaust gas aftertreatment controls (DPF, DOC, etc.).
• EGR valve/EGR cooler modifications.


States Requiring Diesel Emissions Testing

The following states require some form of emissions testing for diesel vehicles. Testing procedures and requirements may vary state-to-state.

• California
• Connecticut
• Colorado
• Arizona
• New York
• Nevada
• Utah
• Tennessee
• Wisconsin