Sources reviewed October 9, 2026
Diesel engines
CARB’s method guidance identifies 2013-and-newer diesel engines for OBD testing. Earlier diesel engines generally use smoke opacity plus a visual inspection.
Alternative-fuel engines
The OBD threshold in that guidance is 2018 for alternative-fuel engines. Earlier alternative-fuel engines use a visual inspection rather than a diesel smoke-opacity test. Special configurations need individual review.
A matching plug is not the whole check
A 9-pin or 16-pin connector tells you how equipment connects. It does not by itself prove the engine, protocol, cable combination and testing service are supported.
Prepare a compatibility request
Have the truck make, engine model year, fuel type and a clear port photo ready. Mention any ELD or telematics equipment already using that port. Ask for the supported configuration before buying a cable or device.