--- title: P0401 and Your Nevada Smog Check | Xpress Smog Check Center url: https://xpresssmogcenter.com/codes/p0401/ 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/) - [Codes](https://xpresssmogcenter.com/codes/) - P0401 # P0401 and your Nevada smog check P0401 means the engine computer commanded exhaust gas recirculation and measured less flow than it expected. EGR exists to cut one kind of pollution, so the code turns on the check engine lamp, and in Nevada a lit lamp fails a 1996 or newer light-duty vehicle at the smog check. 4.7 stars from 550 Google reviews of the two Reno Xpress Oil & Lube Centers Exhaust gas recirculation sounds backward: why would an engine breathe its own exhaust? The answer is temperature. A small, measured amount of exhaust in the intake cools the burn and keeps down the oxides of nitrogen that hot combustion creates. When that flow comes up short, the computer reports P0401, and the smog check reads it. ## At a glance - SAE J2012 defines P0401 as Exhaust gas recirculation (EGR) flow insufficient detected. - EGR lowers combustion temperature to reduce oxides of nitrogen. - A lit lamp fails the Nevada OBD test for 1996 and newer light-duty vehicles. - Removing or disabling emission equipment is tampering, which the DMV says is not eligible for a waiver. ## What EGR does The EGR system routes a little exhaust from the exhaust side back into the intake under certain conditions, usually steady cruising. The inert exhaust takes up space that fresh air and fuel would fill, so the burn runs a bit cooler, and a cooler burn makes less oxides of nitrogen. Some engines meter it with a valve; others manage it with valve timing. The computer checks the system by commanding EGR and looking for the change it should cause, such as a shift in intake pressure or temperature. SAE J2012 names the failure P0401: Exhaust gas recirculation (EGR) flow insufficient detected. In plain words, the computer asked for exhaust to flow and did not see enough of it. ## The smog check side A P0401 car often drives without complaint, and that is beside the point at a Nevada test. The OBD analyzer reads the computer, and a 1996 or newer light-duty vehicle with its check engine lamp on fails. What happens next is set out by the DMV. The failed report documents why the vehicle failed and allows a ten-day movement permit at reduced cost if the registration has expired. It also starts the waiver path, which only counts repairs made after that first failed test. Clearing the code instead resets the EGR monitor and the rest, and gets the vehicle rejected as not ready. ## Common causes a repair shop checks Xpress Smog Check Center tests vehicles; finding the cause is for a repair shop, and the DMV recommends a 2G licensed authorized station for emissions repairs. Common causes a repair shop checks include: - Carbon buildup in the EGR passages, which can choke the flow. - An EGR valve that sticks or does not open fully. - A sensor that reads EGR flow or pressure incorrectly. - A vacuum line or electrical connection to the EGR system that has failed. ## The tampering rule The DMV lists emission device tampering among the conditions that are not eligible for a waiver; the vehicle must be repaired, with no limit on cost. EGR parts are emission control devices. If an EGR system has been blocked off or removed, the repair has to put it back in working order, and no amount of receipts converts that into a waiver. If you are buying a used vehicle, it is worth asking whether its emission equipment is all in place. ## Getting ready for the retest Before you pay for an EGR repair, call the dealer. The DMV advises checking for federal emissions warranty coverage or a recall, since federal law covers some expensive emission components up to 8 years or 80,000 miles. After the repair, the EGR monitor needs the right driving to run, often steady speed on a highway, so give the car up to a week of mixed city and highway driving before you come back. Remove any insurance tracker from the diagnostic port before the test. ## If the lamp is still lit A 1996 or newer light-duty vehicle that still fails for a lit lamp after genuine repairs may qualify for a Washoe County waiver. A 2G station's receipts must show at least $200 in parts and labor directly related to the initial failure, or the owner's receipts at least $200 in related parts bought within 14 days of the initial test. Then the vehicle, both failed certificates and the receipts go to the DMV Emission Lab, which charges nothing for the waiver. ### Sources - [dmv.nv.gov/emission_obd.htm](https://dmv.nv.gov/emission_obd.htm) (Nevada DMV OBD page: lamp on is a fail, test anyway, movement permit, cleared codes, OBD port devices, 8 years / 80,000 miles; read 11/3/26) - [dmv.nv.gov/emission.htm](https://dmv.nv.gov/emission.htm) (Nevada DMV: tampering not eligible for a waiver; Washoe waiver rules; read 11/3/26) - [obd-codes.com/p0401](https://www.obd-codes.com/p0401) (public OBD II code reference: P0401 insufficient EGR flow; read 11/3/26) ### P0401, the generic definition Exhaust gas recirculation (EGR) flow insufficient detected The SAE J2012 code title. The same P0 code means the same thing on every 1996 and newer OBD II vehicle; the cause behind it differs car to car. ### 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) ### Related - [Check engine codes](https://xpresssmogcenter.com/codes/) - [Check engine light and your smog check](https://xpresssmogcenter.com/smog-check/check-engine-light/) - [Repair and retest](https://xpresssmogcenter.com/smog-check/repair-and-retest/) - [Smog waiver in Washoe County](https://xpresssmogcenter.com/smog-check/smog-waiver/) - [Engine swaps and modified vehicles](https://xpresssmogcenter.com/faq/engine-swaps-and-modifications/) 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/) ## More air flow, egr and idle codes [P0101 Mass or volume air flow (MAF) circuit range/performance Learn more](https://xpresssmogcenter.com/codes/p0101/)[P0113 Intake air temperature sensor 1 circuit high Learn more](https://xpresssmogcenter.com/codes/p0113/)[P0411 Secondary air injection system incorrect flow detected Learn more](https://xpresssmogcenter.com/codes/p0411/)[P0507 Idle air control system RPM higher than expected Learn more](https://xpresssmogcenter.com/codes/p0507/) ## If the light is on at your smog check [### Check engine light and your smog check Why a lit check engine light decides the test. Learn more](https://xpresssmogcenter.com/smog-check/check-engine-light/)[### Failed a smog check What the failed report means and the steps that follow. Learn more](https://xpresssmogcenter.com/smog-check/failed-smog-check/)[### Repair and retest Getting the repair done and coming back for the second test. Learn more](https://xpresssmogcenter.com/smog-check/repair-and-retest/)[### Rejected: not ready to test Why a car can be turned away without failing. Learn more](https://xpresssmogcenter.com/smog-check/not-ready-rejected/) ## P0401 questions Still have a question? Call either Reno location or just drive in; there is no appointment to make. ### Can P0401 make my car fail even if the exhaust is clean? Yes. On a 1996 or newer light-duty vehicle the OBD test is decided by the lamp, not by an exhaust measurement. ### Does every car have EGR? Not every engine uses an EGR valve; some manage the same job with valve timing. If your car has stored P0401, its computer monitors EGR flow in some form. ### What does tampering mean for my waiver? The DMV says vehicles with emission device tampering cannot get a waiver and must be repaired with no limit on cost.