--- title: Light-Duty Diesel Testing: Dynamometer and Opacity url: https://xpresssmogcenter.com/guides/diesel-opacity-and-dyno/ business: Xpress Smog Check Center (Located inside Xpress Oil & Lube Center) locations: Reno Northwest: 6100 Mae Anne Ave, Reno, NV 89523, (775) 787-1000, Mon-Fri 8 am-5 pm, Sat 8 am-4 pm, Sun closed; Reno South: 4993 Longley Ln, Reno, NV 89502, (775) 828-6996, Mon-Fri 8 am-5 pm, Sat 8 am-3 pm, Sun closed type: Nevada smog check (vehicle emissions inspection), drive in, no appointment --- Located inside Xpress Oil & Lube Center - Smog check at two Reno locations - Oil change in the same visit - No appointment needed [Xpress Oil & Lube](https://xpressoilandlube.com/) - [Home](https://xpresssmogcenter.com/) - [Guides](https://xpresssmogcenter.com/guides/) - Light-duty diesel testing: dynamometer and opacity # Light-duty diesel testing: dynamometer and opacity In Nevada, a diesel car or truck based in urban Washoe or Clark County with a manufacturer's GVWR of 14,000 pounds or less needs an annual emissions test made up of a dynamometer test, an opacity test and a visual inspection. Heavier diesels have no annual test but face roadside enforcement, and you should call the service center before you bring a diesel. 4.7 stars from 550 Google reviews of the two Reno Xpress Oil & Lube Centers Diesel rules are different from the gasoline rules in three ways: the weight line sits at 14,000 pounds, the test has three parts, and heavy trucks are checked by enforcement officers instead of at a station. This guide explains the rules as the Nevada DMV states them and the terms behind them. For any diesel, call the service center before you bring it. ## At a glance - A diesel needs an annual test if its GVWR is 14,000 pounds or less, it is based in urban Clark or Washoe County, and it is model year 1968 or newer. - The light-duty diesel inspection is a dynamometer test, an opacity test and a visual inspection of emission components. - Diesels over 14,000 pounds GVWR skip the annual test but face statewide roadside enforcement. - Call the service center before you bring a diesel. ## Which diesels need the annual test The Nevada DMV's diesel page lists three conditions that must all be true. The vehicle has a manufacturer's Gross Vehicle Weight Rating of 14,000 pounds or less. It is based in the urban areas of Clark or Washoe County. And it is model year 1968 or newer, with new vehicles exempt for their first three registrations and tested at the fourth. The weight that counts is the manufacturer's rating, which the DMV notes may differ from the declared weight used for registration fees. The simplest check is the renewal notice, which says whether a smog check is required. If you are still not sure, the DMV tells you to contact the Reno or Sahara emission lab, and the Reno lab number is (775) 684-3580. ## The three parts of the test The DMV describes the light-duty diesel inspection as comprehensive, with three pieces: a dynamometer test, an opacity test measuring exhaust density, and a visual inspection of emission components. It is not the plug-in OBD II test that most gasoline vehicles get. The dynamometer is a set of rollers that lets the vehicle be tested while it is held in place. Opacity is how much light the exhaust smoke blocks, which the DMV calls exhaust density. The visual inspection looks at the emission components on the vehicle itself. ## All-wheel drive and traction control Because the vehicle sits on a dynamometer, drivetrain matters. The DMV says some stations can test only two-wheel-drive vehicles or four-wheel-drive vehicles running in two-wheel mode, and that the capability to test full-time all-wheel drive with traction control is limited by station equipment and by wheelbase. If your diesel is all-wheel drive, ask before you drive over, and the DMV's online emission station search is the official place to look up stations. ## Call before you bring a diesel Diesel details depend on the specific vehicle, so the instruction is simple: call the service center before you bring a diesel. Reno Northwest is at (775) 787-1000 and Reno South is at (775) 828-6996. The same call is the right move for a motorhome or a large truck. Our [diesel trucks page](https://xpresssmogcenter.com/faq/diesel-trucks/) and [motorhome and heavy truck page](https://xpresssmogcenter.com/faq/motorhomes-and-heavy-trucks/) collect the common questions. ## Diesels over 14,000 pounds A diesel with a GVWR over 14,000 pounds is not required to participate in the annual smog check program. It is instead subject to statewide roadside enforcement by the DMV Heavy Duty Diesel Enforcement Team, which the DMV describes as sworn peace officers. They conduct traffic stops for observed violations and periodic inspections at highway check sites and weigh stations. The standard is the SAE J1667 snap acceleration test for exhaust opacity. The DMV states that these standards apply to all vehicles traveling in Nevada, including those registered in other states. ## Waivers for diesels The DMV's diesel page points to a separate document, form EC 004, for the waiver requirements that apply to light-duty diesels that still fail after repairs. The general rules still hold: a failed test starts the process, money spent before the first failed test does not count, and a vehicle that smokes cannot be waived. Read the EC 004 form or call the Reno emission lab before you spend money on a repair. ## Validity and timing As with gasoline vehicles, a standard diesel result is valid for 90 days, and 180 days if the vehicle was bought from a Nevada dealer. Testing early leaves time for repairs before the registration deadline, which matters more for a diesel because its repairs can take longer to arrange. ### Sources - [dmv.nv.gov/emission_diesel.htm](https://dmv.nv.gov/emission_diesel.htm) (Nevada DMV Diesel Testing and Enforcement: weight line, test parts, roadside enforcement; read 10/19/26) - [dmv.nv.gov/emission.htm](https://dmv.nv.gov/emission.htm) (Nevada DMV Emission Control Program: exempt list, validity, fees; read 10/19/26) - [dmv.nv.gov/pdfforms/ec004.pdf](https://dmv.nv.gov/pdfforms/ec004.pdf) (Nevada DMV diesel emissions requirements and waiver form EC 004; read 10/19/26) ### Your location: Reno South - Call [(775) 828-6996](tel:+17758286996) Mon-Fri 8 am-5 pm, Sat 8 am-3 pm, Sun closed - Address 4993 Longley Ln, Reno, NV 89502 [Directions](https://www.google.com/maps/dir/?api=1&destination=4993+Longley+Ln%2C+Reno%2C+NV+89502&destination_place_id=ChIJc5xNCcI_mYARXjHn3y79iJw) Located inside Xpress Oil & Lube Center Both smog check locations sit inside an Xpress Oil & Lube Center, the locally owned Reno drive-in that has served this town since 1983. Drive in, no appointment; get your oil changed in the same visit. [About us](https://xpresssmogcenter.com/about/) ### Keep reading - [Diesel smog check rules](https://xpresssmogcenter.com/smog-check/diesel-smog-check/) - [Diesel truck questions](https://xpresssmogcenter.com/faq/diesel-trucks/) - [Motorhomes and heavier gas trucks](https://xpresssmogcenter.com/faq/motorhomes-and-heavy-trucks/) - [The Nevada smog check, explained](https://xpresssmogcenter.com/guides/nevada-smog-check-explained/) - [Smog check glossary](https://xpresssmogcenter.com/glossary/) - [Locations](https://xpresssmogcenter.com/locations/) ## Questions people ask Still have a question? Call either Reno location or just drive in; there is no appointment to make. ### My diesel pickup is a three-quarter ton. Does it need a test? It depends on the manufacturer's GVWR. At 14,000 pounds or less and based in urban Washoe, yes. Check the renewal notice and call the service center before you bring it. ### Is a diesel test the same as a gasoline smog check? No. A light-duty diesel gets a dynamometer test, an opacity test and a visual inspection of emission components. ### Do out-of-state diesel trucks face the roadside rules? The DMV says the heavy-duty standards apply to all vehicles traveling in Nevada, including those registered in other states.