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Periodic Smoke Inspection Program
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Periodic Smoke Inspection Program

The Roadside Anti-Smoke Inspection

The Periodic Smoke Inspection “Fleet” program serves as a companion to the Heavy Duty Diesel Inspection Roadside program. CARB staff will select a vehicle at random and direct them to a roadside inspection station. Some of the keys steps in the inspection include:

  • RPM Recording: The inspector records the vehicle’s RPM at idle and at maximum governed speeds.
  • The Snap-Acceleration Test: The inspector positions a smoke sensing meter just above, or places a probe inside the vehicle’s exhaust pipe. The driver then rapidly accelerates the engine three times, with the transmission in neutral, to clear the exhaust of loose particles. The driver is then instructed to repeat the snap-acceleration test three times. The meter measures the opacity of the smoke being emitted.

Allowable Levels of Smoke Opacity

All 1991 or newer engines: Must not exceed 40% smoke opacity.
All pre-1991 engines: Must not exceed 55% smoke opacity.

The Visual Inspection:


The inspector looks under the hood to check for visible signs of tampering, to record engine data and to ensure the engine has the appropriate emission control label (ELC).


Inspection Requirements

All California based fleets of two or more heavy duty vehicles (GVWR of 6,000 or more pounds) are required to perform annual smoke and tamper inspections of their fleets. Fleet owners are not required to inspect diesel vehicles until the fourth year of engine model year. An example of this would be a 2000 model year engine must have first test completed by January 1, 2004.


It is our goal to educate all involved to prevent companies from being fined for non-compliance. Please contact us at your earliest convenience at (877) 574-8289. We look forward to hearing from you soon.

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