Skip to main content

Preparing for a Smog Test: Top 5 Myths and Tips

I've worked at a smog check station in Sacramento, and I hope to shed light on scams/tricks people use to pass the smog check.

The Dreaded California Smog Inspection

In California, the law requires you to smog check your vehicle once every two years, or if your vehicle is tagged as a high-polluting vehicle, once a year. The smog check is mandatory; if you don't do it, you can't complete your next year’s registration. This, in turn, means that you are not allowed to legally drive your car in California.

I have experience working at a smog check station in Sacramento, and I hope to shed light on a few scams and tricks people use to supposedly help you pass the smog check with flying colors. Hopefully, you will learn something new and avoid getting scammed into buying products or parts you don't need.


Myth 1: You Should Warm Up Your Car at High RPMs Before Getting It Smogged

Should you warm up your car at high RPMs before getting it smogged? The answer is yes and no.

Let's start with the "yes" part. Warming up your car does get your motor running in its best overall condition and allows your catalytic converter to work at the proper level. So yes, having a warmed-up vehicle does help to pass the smog check.

Now, the "no" part of the answer. As a practical matter, it doesn't do any good to warm up your car before a smog test. Supposing you do follow this suggestion and sit in your car for five minutes at 3000 RPM, before handing the keys to the smog tech. Then, more than likely, at least 10 minutes will pass before the check begins, and in those 10 minutes your catalytic converter has cooled off and the effect of anything "extra" you have done to warm up your car is gone. You have only wasted time and gas, and looked like a fool sitting in your car warming it up.

Myth 2: Fuel Cleaners and Octane Boosters Help You Pass the Test

Do fuel cleaners and octane boosters help? Again, the answer is yes and no.

Fuel cleaners will help your car’s engine get clean. This means that a mass of gunk stuck to your engine's valves and head is going to get removed. To get it removed it must be burned, and to be burned it goes into your cylinder head and releases different types of emissions. It's a good idea to use a fuel cleaner often, but it's a bad idea to put it in the car for the first time right before you are taking your car to get smogged.

Octane boosters are another suggestion that won't help you pass a smog test. They enrich the fuel of your car, meaning the engine will burn the fuel, any additives, and anything else at hand. Anything burning inside the motor leaves via the tail pipe, and any new stuff in the mix might cause you to fail your tail pipe emissions test. So don't use these additives right before a smog test.

Myth 3: You Need a Tune-up to Pass

Actually, more often than not, this myth is true. If your car is not running right, or is misfiring, it will most likely fail the smog test. If you have a bad misfire, this could cause your check engine light to come on also, meaning you will fail the functional portion of the smog inspection.

Getting a tune-up is usually a plus in more than one way. Not only will it increase your chance of passing a smog test, but your vehicle will also run a lot smoother and you'll get more miles per gallon. Simple changes to the operation of your spark plugs, wires, cap, and rotor, and replacing the air filter and fuel filter when needed, can really make a big difference. Follow the manufacturer's recommendations on when to maintain your vehicle and keep your car running in prime condition.

Catalytic Converter or "Cat"

Catalytic Converter or "Cat"

Myth 4: All You Need to Do Is Replace the CAT

Many smog check places make this suggestion, but replacing your CAT (catalytic converter) is usually one of the last things that you should mess with. Get advice and find out exactly what the problem is before okaying the replacement of an expensive part.

Your smog technician may be recommending a cat just to make a quick fix so that your car will pass this week. But you may find in succeeding years that each time you take your vehicle for a smog inspection, it will either need a catalytic converter to pass, or it will fail for sure.

I suggest that you take your vehicle to a licensed smog repair shop, and have them diagnose the issue correctly. If your catalytic converter is going bad, something is causing it to go bad. Rather than just replace your catalytic converter each time, identify and fix the problem.

"Check Engine" light (yellow motor icon) on dashboard

"Check Engine" light (yellow motor icon) on dashboard

Myth 5: You Should Pull Out Your "Check Engine" Light Before the Smog Check

This is one of the most common things people try to do to get their car to pass, and one of the silliest. Most vehicles from 1990 and later are equipped with a check engine light. This light is required to be working when the technician tests the vehicle. If the tech doesn't see the light, he must check his book to see if the vehicle comes with a light. If your vehicle comes equipped with a check engine light, but it does not work—either because it went out or because someone tampered with it—your car will automatically fail.

Make sure your check engine light works. On GM cars, the light is a little legend, "Service engine soon," and on most other makes it's a little yellow engine-shaped light. If your check engine light stays on, it means that for some reason your engine is not running in the cleanest and most economical way, and so you may as well have your car serviced.

Final Thoughts

I hope you learned a few ways to make sure you do not fail your smog inspection. Always follow the manufacturer's guidelines for service intervals. Make sure that you don't do something that could ruin your vehicle's smog history, since it stays with your car forever.

California Smog Certificate

California Smog Certificate

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2011 biggking