Clean Truck Check recognises two testing procedures. Which one applies to your vehicle is decided by whether it has an on-board diagnostics system — not by its size, weight or the work it does.
OBD testing
For vehicles with OBD systems, emissions data is read straight from the onboard computer. The test confirms that the emissions controls are present, connected and working. It is fast, and because it is a data pull rather than a measurement, results are unambiguous.
Who this applies to
Broadly, engines from the 2013 model year onward. These are also the vehicles moving to quarterly testing in October 2027.
Opacity testing
Older vehicles without OBD are measured instead: a smoke opacity test gauges the density of the exhaust, which stands in as a proxy for particulate emissions. It is a physical measurement, so a poorly maintained vehicle will show it.
What both have in common
- The test itself is performed at a CARB-authorized facility.
- The result still has to be reported through CTC-VIS to count.
- A passing test that is never filed leaves you non-compliant on paper.
That last point is where most avoidable trouble starts. Testing and reporting are two separate steps, and only one of them happens at the shop.
