Diesel smog check rules

Diesel pickups are everywhere in northern Nevada, and the DMV treats them differently from gas vehicles in two ways: weight decides whether they test at all, and the test itself is more involved. Here are the rules from the DMV's diesel page.

At a glance

• Tested: diesels with a manufacturer's GVWR of 14,000 pounds or less, based in urban Washoe or Clark (Nevada DMV).
• New diesels test from their fourth registration.
• Light-duty diesel test = dynamometer + opacity + visual inspection of emission components.
• Over 14,000 pounds: no annual test, but statewide roadside enforcement.

The weight line

For diesels, the DMV's test requirement turns on the manufacturer's gross vehicle weight rating. A diesel with a GVWR of 14,000 pounds or less, based in the urban areas of Washoe or Clark county and 1968 or newer, needs the annual test. Above that, it does not.

The DMV adds a detail that trips people up: the manufacturer's weight rating decides, and it may differ from the declared weight you use for registration fees. Your renewal notice says whether a smog check is required. Most full-size diesel pickups, including the heavy-duty three-quarter and one-ton models, have GVWRs under 14,000 pounds and do test.

How a light-duty diesel is tested

The DMV describes the light-duty diesel inspection as three parts: a dynamometer test, where the truck runs under load on rollers; an opacity test, which measures how dense the exhaust is; and a visual inspection of the emission components.

That equipment is not part of the OBD test gasoline cars get, so not every station tests diesels, and the DMV notes that some stations can only test two-wheel-drive vehicles or four-wheel drives running in two-wheel mode. Call the service center before you bring a diesel, and have your year, make, model and drive type ready.

New diesel trucks

New vehicles are exempt for their first three registrations, diesels included. The test starts at the fourth registration.

Heavy diesels and the roadside rule

Diesel vehicles over 14,000 pounds GVWR are not part of the annual smog check program, but the DMV's Heavy Duty Diesel Enforcement Team, made up of sworn peace officers, enforces air quality standards statewide. Officers conduct traffic stops for observed violations and periodic inspections at highway check sites and weigh stations, using the SAE J1667 snap acceleration test for exhaust opacity. The standards apply to every vehicle traveling in Nevada, including trucks registered in other states.

Validity and renewal

A diesel test is valid 90 days for most purposes and 180 days when the vehicle was bought from a Nevada dealer. Like any test, the result goes to the DMV electronically.

If you are not sure whether your diesel needs a test, the DMV suggests contacting the Reno emission lab at (775) 684-3580.