OBD or opacity: which test does my truck need?

What the OBD test checks

The OBD test reads information from the electronic emissions system using a CARB-certified device. CARB says OBD-equipped diesel engines of model year 2013 or newer require this test. Reading codes with an ordinary shop scanner is not the same as a compliance test: the program requires the specified equipment and a credentialed tester.

What the opacity test checks

For diesel vehicles without applicable OBD—generally engine model years 2012 or older—CARB requires a smoke-opacity test plus a visual inspection of emissions-control equipment. Opacity measures exhaust smoke; the visual inspection checks required components.

How to avoid an unsuccessful visit

Have the VIN, year, and engine information ready. Check CTC-VIS and confirm the test type with a credentialed tester. If fault codes or a Check Engine light are present, investigate the cause before clearing data.

An OBD test can return “Not Ready” after codes are cleared or the battery is disconnected. CARB recommends normal operation and a retest once readiness criteria are met, rather than clearing codes just before an appointment.