California requires most vehicles, including heavy-duty trucks, to undergo smog checks periodically to ensure they meet state emissions standards. Heavy-duty trucks are generally exempt from smog checks if they:

Operate on diesel fuel

Have a gross vehicle weight rating (GVWR) of more than 10,000 pounds

Are registered as commercial vehicles

However, some older diesel trucks and heavy-duty vehicles not registered as commercial may still be subject to smog check requirements. In addition, some areas of California may have stricter emissions regulations that require heavy-duty trucks to undergo smog checks, regardless of their size or weight.