Diesel Smog Check in California

California certified smog check stations are allowed to perform a diesel engine smog inspection if they possess OIS Smog Test equipment. The diesel smog test will not include the emissions test portion of the regular inspection. There will be no tailpipe emissions inspection either.

Diesel cars and trucks are not driven on a dynamometer during the smog test either.

The diesel smog test will focus on a visual inspection of your vehicle's emissions/smog components, a system check of the On Board Diagnostics (OBD II) system, and a smoke check for visible smoke from the PCV system or smoke plume observed 3 to 15 feet from the tailpipe(s) that lingers for more than 3 seconds. Diesel cars and trucks which fail the diesel smog test will have to get their vehicles repaired at a diesel vehicle repair shop before retesting.

Diesel smog inspections are required during a diesel vehicle's initial registration in California and once, every two years, thereafter. The diesel smog check cycle will continue for as long as the vehicle is registered in this State.

Number of incomplete monitors allowed to pass on diesel powered vehicles:

• Old standard: any two for 1998 to 2000 model years
• New standard: zero for 1998 to 2006 (OIS test)
• Old standard: any one for 2001 & newer model years
• New standard: any two for 2007 and newer (OIS test)

The Diesel smog test program applies to 1998 and newer passenger vehicles and trucks powered singly or in combination by:

• Gasoline
• Propane
• Natural gas
• Diesel
• Methanol / Ethanol fuels

Smog inspections are also required anytime a diesel vehicle is sold or bought in California. During a title transfer the Department of Motor Vehicles will not allow a vehicle to be registered unless it is presented with a valid smog certificate.

There are special testing procedures for vehicles, which are classified as "Gross Polluters". These include Test Only and State Referee inspections.