Before you take your car in for a smog check, is there anything you can do to give it a better chance of passing? Here are some simple steps you can take to tilt the odds of passing a smog check in your favor:

Make sure the engine is warmed up.  Before you drop off your car at the inspection station, make sure it is warmed up.  A drive for 10-15 minutes should ensure that.  Then all mechanical systems are operating at the temperatures they are designed to operate at and emissions will be at a minimum.

Is the "Check Engine" light on? If your car displays the Check Engine light, that's an automatic failure for most state inspections. The most common reason for a Check Engine light being illuminated is a faulty oxygen sensor.  There are many other reasons that a check engine light can be illuminated but you should have your mechanic look at it before you bring in your car for a state inspection.

Drive the car at highway speeds for a week prior to the smog test. This gets the catalytic convertor hot enough to burn off any oil and gas residues. By driving the car at highway speeds for a while, the catalytic convertor will burn off residues that could cause you to fail your smog test.

Make sure the tires are properly inflated. Many states require a dynamometer test which positions the car's tires on rollers that allow the engine to run at highway speeds while it is stationary. If the tires are under-inflated, the car's engine works a little harder to achieve the engine revolutions required by the test.  

Change the oil (but only if it needs it). Dirty oil in the crankcase can release additional pollutants which could cause the car to fail the smog test.

Use a fuel additive. Older cars could have clogged fuel injectors causing them to run lean. Injector additives can clean the small openings and help the car pass the smog test.


Deery Brothers of Ames, Inc.

1700 SE 16th Street
Directions Ames, IA 50010-6430

  • Sales: 515-337-2515
  • Service: 515-520-8406
  • Parts: 515-598-7353


  • Monday 8:30 am - 7:00 pm
  • Tuesday 8:30 am - 6:00 pm
  • Wednesday 8:30 am - 7:00 pm
  • Thursday 8:30 am - 7:00 pm
  • Friday 8:30 am - 6:00 pm
  • Saturday 8:30 am - 5:00 pm
  • Sunday Closed