--- title: "Clean Truck Check OBD Test vs Smoke Opacity Test: Which Does My Truck Need?" description: "Diesel trucks 2013 and newer and alternative-fuel trucks 2018 and newer get an OBD scan; diesel 2012 and older get a smoke opacity (SAE J1667) test plus visual…" url: "https://ctcfinder.com/guide/obd-vs-smoke-opacity-test/" updated: "2026-11-01" publisher: "CTC Finder (independent directory, not affiliated with CARB)" --- # OBD test or smoke opacity test: which Clean Truck Check test your truck needs Updated 2026-11-01. Source: CTC Finder (https://ctcfinder.com/guide/obd-vs-smoke-opacity-test/). Independent; not affiliated with CARB. **Short answer:** It depends on model year and fuel. **Diesel 2013 and newer** and **alternative fuel 2018 and newer** get an **OBD test**: a credentialed tester plugs a CARB-certified device into the diagnostic port, which takes a few minutes. **Diesel 2012 and older** get a **smoke opacity test (SAE J1667) plus a visual inspection**, which needs a smoke meter. **Alternative fuel 2017 and older** get a **visual inspection only**. Published prices are usually $50–$135 for an OBD test and $190–$200 for smoke opacity. ## Which test, by vehicle | Vehicle | Test | Typical published price | |---|---|---| | Diesel, model year 2013 and newer | OBD scan with a CARB-certified device | $50–$135 | | Alternative fuel, model year 2018 and newer | OBD scan | $50–$135 | | Diesel, model year 2012 and older | Smoke opacity (SAE J1667) plus visual inspection | $190–$200 | | Alternative fuel, model year 2017 and older | Visual inspection only (no smoke test) | Ask the tester | From **October 2027**, OBD trucks test four times a year; smoke opacity trucks stay at twice a year. See [what changes in 2027](https://ctcfinder.com/guide/clean-truck-check-2027/). ## What happens during an OBD test 1. The tester connects a CARB-certified OBD device (handheld or telematics) to the truck's diagnostic port with the key on. 2. The device reads the engine's emissions data: fault codes, readiness monitors and identification. 3. The result goes to CARB. With a credentialed tester's telematics device the upload is automatic. **Common reasons an OBD test fails or cannot finish:** an active check-engine light or emissions fault code, readiness monitors not yet set after a repair or battery disconnect, or a VIN mismatch. Some testers offer a cheaper **pre-check** scan first. CARB-certified handheld devices include RA Consulting Silver Snap-Tool, HEM Data DAWN OBD Inspector, Noregon Truck Check Up, DG Technologies DPA INSPECT and Opus Clean Truck kit. Certified telematics devices include Geotab GO9, Pacific Track PT40, Zonar V4/VT4, Samsara VG, Verizon Connect (Xirgo) and Motive Vehicle Gateway. ## What happens during a smoke opacity test 1. **Visual inspection** of emissions-related equipment (for example, that the diesel particulate filter and other parts are present and not tampered with). 2. **Smoke opacity test** under SAE J1667 (the "snap acceleration" test): the engine is revved quickly several times while a smoke meter measures exhaust opacity. 3. The tester submits the result through their CTC-VIS tester account. Fewer testers own a smoke meter, which is why opacity tests cost more. 1,223 of the 2,867 testing businesses we list in California say they do smoke opacity tests; use the **Smoke opacity** filter on any [city page](https://ctcfinder.com/testers/). ## What to bring or have ready - VIN, license plate and odometer reading. - The vehicle reported in CTC-VIS and the annual fee paid ([how to register](https://ctcfinder.com/guide/how-to-register-ctc-vis/)). - A warm engine and no active warning lights. - For a mobile test: a safe, level spot at your yard with access to the cab (and, for opacity tests, the exhaust). ## Shop or mobile? An OBD test needs no special bay, so many testers come to you, and OBD trucks can also be tested with a CARB-certified telematics device ([remote and telematics testing](https://ctcfinder.com/guide/remote-and-telematics-testing/)). 2,543 of the businesses we list offer **mobile testing**. Mobile is usually a little more per truck for one vehicle but cheaper per truck for fleets. [Find mobile testers](https://ctcfinder.com/mobile-testers/) or [get quotes for several trucks](https://ctcfinder.com/get-quotes/). ## Frequently asked questions ### How long does a Clean Truck Check test take? An OBD test takes a few minutes per truck once the device is connected. A smoke opacity test with visual inspection takes longer because the engine must be warmed up and revved several times. ### Can I do the OBD test myself? Only if you are a CARB-credentialed tester. Owners can get credentialed through CARB's free online course and exam and then test their own trucks with a certified device. ### Does my 2012 diesel truck need an OBD test or smoke test? Diesel trucks with model year 2012 and older get a smoke opacity test (SAE J1667) plus a visual inspection. ### Why did my truck fail the OBD test? Usually an active emissions fault code, readiness monitors that are not set (common right after a repair or battery disconnect) or a VIN mismatch. Fix the fault, drive until monitors are ready and retest. ## Sources - CARB, [Requirements for vehicles subject to semi-annual compliance](https://ww2.arb.ca.gov/clean-truck-check-requirements-vehicles-subject-semi-annual-compliance) - CARB, [CARB-certified OBD test devices](https://ww2.arb.ca.gov/our-work/programs/inspection-and-maintenance-program/obd-test-devices) - CARB, [Clean Truck Check FAQ](https://ww2.arb.ca.gov/resources/fact-sheets/clean-truck-check-faq-0) - Published tester prices: see the [cost guide](https://ctcfinder.com/guide/cost/)