California's three step emission inspection procedures consists of:
1) Visual inspection of the engine's emissions control equipment, including (but not limited to) the EGR, DPF, PCV, and SCR systems.
2) An OBDII (onboard diagnostics system) inspection in which the condition of the onboard diagnostics system is checked in addition to identification of any present diagnostic trouble codes (DTC).
3) A visible smoke test from the tailpipe and crankcase (smoke opacity test or "snap test").
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.
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), diesel oxidation catalyst (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: California, Connecticut, Colorado, Arizona, New York, Nevada, Utah, Tennessee, Wisconsin (testing procedures and requirements may vary state-to-state).