Indian School: (623) 848-1970
Cave Creek Rd: (602) 888-2277

Six Factors That Could Affect Your Car’s Smog Test Results

Requiring a smog test is a vehicle law put in place for a couple reasons—to ensure your vehicle is performing correctly, and to better protect the environment against pollution. Unfortunately, when it comes to smog checks, some vehicles run into an issue—they fail the test. This is often the case for older vehicles and vehicles that have sat parked for a long time, while other factors can also be contributors.

Below, a professional mechanic in Phoenix shares with us some factors that could negatively affect your car’s smog test results:

  • Engine is cold: One of your best bets at passing a smog test the first time is taking it in after the engine has been warmed—avoid arriving at your smog check station with a cold engine. Driving around for at least 20 minutes before getting the smog check ensures the engine is warm, and also provides a chance for the fuel to move around and reach proper combustion levels.
  • Oil needs to be changed: Failing a smog test can be the result of something as simple as dirty or contaminated motor oil. Dirty oil can greatly affect smog test results, because the fumes from the oil compartment emanate throughout the engine area and become a part of the engine’s combustion. Remember to change the oil before getting a smog check.
  • Tires not properly inflated: A smog test technician will leave your vehicle running automatically on a stationary machine used to obtain various readings. You must be sure your tires are inflated properly so it drives evenly and stably during the test. Deal with uneven tire pressure at home by using a portable air pump, or head to the gas station and use their air.
  • Catalytic converter is malfunctioning: It’s not unusual for an older vehicle to go through several catalytic converters in its lifetime. Many aftermarket cats are built to last three to five years before needing to be replaced again; otherwise, you are likely emitting emissions through the muffler. Needless to say, if your vehicle is emitting a ton of emissions during the test, it is not going to pass.
  • Check engine light is on: A huge indicator of a potential smog test fail is going into the testing station with the “check engine” light on. In some cases, and in some states, a smog technician might refuse testing on vehicles with an illuminated check engine light, often resulting in an automatic fail.
  • Repairs are needed: Any major problems under the hood will increase the likelihood of your vehicle failing a smog test—especially if there are problems with the engine. Simply put, to significantly increase your car’s chance at passing, don’t schedule a smog check until major repairs have been completed.

Needing to get a smog check can be annoying, but don’t ignore the DMV’s request. This can cause a delay in receiving your new vehicle registration tags, and may even require you to have to jump through hoops with your insurance company. At S & J Auto Repair & Rental, we do smog testing and offer emissions repair. Call to schedule an appointment with a professional mechanic in Phoenix today!

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Indian School Location:
(623) 848-1970
Scottsdale Location:
(480) 590-4397
32nd Location:
(602) 935-3551
Glendale Location:
(602) 888-2277
Cave Creek Rd Location:
(602) 888-2277
7th Street Location:
(480) 686-8125