Opacity Testing (SAE J1667) — Who Needs It and Why

Engine Year 2012 and Older • Not the Vehicle Year

Straight answer up front: we perform OBD testing, not opacity testing.

Here's how to tell which one your truck needs — before anyone drives anywhere.

What We Do and Don't Do

We're a CARB-credentialed mobile tester covering Napa, Sonoma, and Solano counties, and we perform OBD emissions testing — the scan required for 2013 and newer diesel engines and 2018 and newer alternative-fuel engines.

We do not currently perform SAE J1667 smoke opacity testing. That test requires a certified smoke meter, which is a significant piece of equipment, and we haven't added one to the truck yet. It's on the list.

We're putting that on its own page because the alternative is you booking a test we can't perform, waiting for us, and then finding out in your own yard. That's a bad afternoon for both of us.

If your engine turns out to be 2012 or older, call anyway — we'll confirm it from the label and point you at someone who can help. No charge for that, obviously.

Quick Reference

  • 2013+ diesel engine → OBD scan (we do this)
  • 2012 or older diesel → J1667 opacity (we don't)
  • 2018+ alt-fuel engine → OBD scan (we do this)
  • 2017 or older alt-fuel → visual inspection
  • Engine year, never vehicle year
  • Not sure? Text us a photo of the label

OBD vs. Opacity, Plainly

The OBD Test

  • A data read from the engine computer
  • Checks fault codes and readiness monitors
  • Takes 15-20 minutes, engine stays at idle
  • Required for 2013+ diesel engines
  • This is what we perform

The J1667 Opacity Test

  • A physical measurement of visible smoke
  • Snap-acceleration from idle to governed speed
  • Calibrated smoke meter reads the plume
  • Result is an opacity percentage vs. a limit
  • Required for 2012 and older diesel engines

Finding Your Engine Year

  • Look for the emissions control label
  • Usually on or near the valve cover
  • Lists engine family and model year
  • Often differs from the vehicle year
  • Text a photo to 707-225-7982

One Advantage of an Older Engine

If your truck is on the opacity side of the line, there's a genuine upside coming.

From October 2027, OBD-equipped vehicles move from twice-yearly testing to four times a year. Older, opacity-tested engines are not included in that change — they stay on the semi-annual schedule.

So a 2012 engine costs more per test but gets tested half as often from late 2027 onward. Worth putting in the spreadsheet if you're weighing whether to replace an older unit.

Whichever side you're on, the 90-day early-submission window works the same way: you can file a passing result up to 90 days before your deadline, which is the margin that saves you if something fails.

Where to Go From Here

Schedule Your Clean Truck Check

Fill out the form below and we'll get back to you promptly — or call 707-225-7982 and skip the form.

Common Questions

No — not currently. We perform OBD testing for 2013 and newer diesel engines. A J1667 opacity test requires a certified smoke meter, which is a substantial piece of equipment we haven't added yet. We'd rather say so plainly on this page than have you find out after we've driven to your yard.

The engine model year decides it, not the vehicle year. Diesel engines from 2013 and newer take an OBD scan. Diesel engines 2012 and older need a SAE J1667 smoke opacity test. Alternative-fuel engines from 2018 and newer take an OBD scan, and 2017 and older alternative-fuel engines get a visual inspection instead. Check the emissions control label on the engine — the engine year is often a year or more off the vehicle year.

It's a snap-acceleration smoke test run to the SAE J1667 standard. With the vehicle stationary, the engine is revved from idle to governed speed several times while a calibrated smoke meter measures how much light the exhaust plume blocks. The result is an opacity percentage, and it's compared against the limit for your engine's age and type. It's a physical measurement of visible smoke, where an OBD test is a data read from the engine computer.

Expect noticeably more than an OBD scan — published rates from mobile testers serving Northern California currently run in the range of roughly $200 to $250 per vehicle, against $75 to $125 for an OBD test. The equipment is expensive and the test takes longer, and that's reflected in the price. Get a couple of quotes.

Call us anyway at 707-225-7982. We'll confirm from your engine label which test you actually need — a fair number of people who think they need opacity testing turn out to have a 2013 or newer engine — and if you genuinely need a smoke test we'll point you toward someone who does them. It costs you nothing and it beats guessing.