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.
What happens during an OBD test
- The tester connects a CARB-certified OBD device (handheld or telematics) to the truck's diagnostic port with the key on.
- The device reads the engine's emissions data: fault codes, readiness monitors and identification.
- 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
- Visual inspection of emissions-related equipment (for example, that the diesel particulate filter and other parts are present and not tampered with).
- Smoke opacity test under SAE J1667 (the "snap acceleration" test): the engine is revved quickly several times while a smoke meter measures exhaust opacity.
- 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.
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).
- 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). 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 or get quotes for several trucks.
Sources
- CARB, Requirements for vehicles subject to semi-annual compliance
- CARB, CARB-certified OBD test devices
- CARB, Clean Truck Check FAQ
- Published tester prices: see the cost guide
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.
CTC Finder is an independent directory and is not affiliated with CARB. Rules change; check CARB's Clean Truck Check pages for the official version.