The smog check came back not ready

This week

General guidance for this symptom. A warning light that is flashing or an overheating engine: stop driving and call.

Likely causes

• A battery was disconnected or replaced

  Disconnecting power clears the computer's memory, including the monitor results. They start again from zero.

  Battery check
• Codes were cleared after a repair

  Clearing a check engine light with a scan tool also clears readiness. If the original fault is fixed, the monitors complete with normal driving.

  Smog check and emissions test
• Short trips only

  Some monitors, especially the evaporative system and catalyst monitors, need specific conditions: a cold start, steady highway speed, a certain fuel level or a long idle. A car that only does short trips across town may not hit them.

  Smog check and emissions test
• An underlying fault keeps a monitor from finishing

  If a fault is still present, the related monitor may never complete. A repair shop with a scan tool can see which one is stuck and why.

  Multi-point maintenance check

A not-ready result is not a failure in the usual sense. In Nevada's testing area, newer vehicles are checked through the onboard diagnostic system, and that system has to report that its own checks are complete. A recently disconnected battery, a code cleared by a scan tool, or a repair that reset the computer wipes those results, and the car needs time on the road to run them again. The EPA describes this as the OBD system confirming that emissions components were monitored.

Helping the monitors finish

1. Keep the fuel tank between about a quarter and three quarters full; some evaporative monitors need that range.
2. Start the car cold at least once a day, after it has sat overnight.
3. Include some steady highway driving, for example a run on I-80 or US-395 at a constant speed.
4. Include some city driving with stops and a few minutes of idle.
5. Repeat over several days. Some monitors finish in one drive, others take a week of mixed driving.

Your owner's manual or the manufacturer may publish a specific drive cycle. Following it can speed things up. Our readiness monitors guide goes deeper.

The Nevada rules that apply

Smog checks are required at registration renewal for gasoline vehicles 1968 and newer and diesels up to 14,000 lb in the Washoe County and Clark County testing areas. New vehicles are exempt for their first three registrations, and hybrids for their first five model years (Nevada DMV emission program). Carson City, Douglas and Lyon County registrations do not require a test.

A passing test is valid for 90 days, so you do not need to cut it close. Test as soon as the monitors are ready, then renew. If your renewal date is near, the DMV page explains the options, and our renewal steps guide lays out the order.

What our Reno service centers do

Our Mae Anne and Longley Lane service centers run the smog check. When a car comes back not ready, we tell you which monitors were incomplete, so you know what kind of driving to do. You can come back without an appointment when you are ready.

If a monitor will not complete because of a fault, that is repair shop territory. We do not do emissions repairs. Once the repair is done and the car has been driven enough, drive back in for the test.