How to Get Your Car to Pass the Emissions Test


If your worried about your car passing the yearly emissions inspection, this article will show you how to prepare your car to pass the emissions inspection.

”In order to pass the emissions test you have to change your engine oil, make sure your air filter is clean, make sure your spark plugs are in good shape, check your cooling system and AC fans and if needed, try pouring fuel injection cleaner into the gas tank.”

Many places require that every year you have your car inspected in order to get the inspection sticker on your windshield. Part of the test is a safety test. Checking things like tires, to make sure they’re not bald and brakes work okay, and to make sure that your headlights work. Now, that stuff’s pretty cut-and-dry and anybody can check it. But, when it comes to emissions inspection, since your nose can’t really tell what’s coming out of the tailpipe, there’s a few preventive measures you can do to make sure it passes the emissions testing. On older cars, they actually measure the gas that comes out of the tailpipe with a dynamo-meter test, so you want to make sure everything is working fine, so the gases that come out of the pipe, are very low and aren’t polluting much.

Engine Oil

So, first make sure that the oil is clean. Change the oil and filter before your inspection, because if the oil gets dirty, the PCV system can suck a lot of those dirty vapors in, burn them, and pollute more. And of course you want to have clean oil anyway, but right before the inspection is the best time to have the cleanest oil.

See my Beginners Guide – How To Change Engine Oil

Air Filter

The next thing to do is, to make sure the air filter is clean. If you have a dirty air filter, it’ll block the air, the car will run lean, and it’ll pollute too much. A lean running car makes the engine run hotter, the exhaust gases get hotter, puts out more NOx, which is a pollutant they measure, and you can fail the test.

Spark Plugs

Check your spark plugs to make sure they’re in good shape. Spark plugs have a gap where the electricity fires, and when it’s old and worn out, when the gap is too big and they don’t work right (even if a car is running okay if the gap is too big), it’ll pollute more and you’ll fail the test.

Cooling System

You would want to check the cooling system, because if the coolant is low, the top of the engine will get air in it, make it run hotter and it’ll pollute more. You need to realize that the engine doesn’t have to be overheating on the gauge to make part of the engine still running too hot. So, make sure it’s full of coolant and that it’s clean.  And of course, make sure that the cooling fans are working correctly. Turn on the AC on full blast and make sure that the fans are spinning. Because the test takes place on a dynamometer, the car isn’t moving, if those cooling fans aren’t sucking air, the engine will run hotter and it can fail the test.

See my article: How To Flush A Cooling System

Engine Light On

Now, if you have a more modern car, they don’t test them on a dynamometer, they just plug into the computer to see if there’s a problem. All cars from 1996 on are tested this way. So, if you have a 1996 or newer car and a check engine light is on, you need to fix it before you go to get inspected. That means there’s a trouble code stored in the computer and when they inspect it, their computer will fail it for the test. There are over 2,000 separate trouble codes that can exist in a car, so it can get really complicated when a light comes on.

Fuel Injection Cleaner

Let’s say that you’re unlucky and you’ve already done everything, and your car still fails the emissions test. Well, you can try fuel injection cleaner. Pour it in the gas tank, and drive the car really hard on the highway, about 70 or 100 miles. Personally I’ve had very good luck using the shop line solvent, I just pour a gallon of the solvent to about half a tank of gasoline, then I go on a highway and drive the car at the maximum speed limit, for about half an hour or 45 minutes. You can get fuel injection cleaner on I’ve done this on many cars and got them to pass the emissions test after doing this. Of course, this is not a magic fix. If the car doesn’t run good, it’s got a serious problem that needs to be fixed, but if the car runs okay, this can often let it pass the test, because the solvent burns really clean, so the gas coming out of the exhaust can get cleaner and cleaner as it cleans all the systems out. If you have a late model code with a check engine light, and it says inefficient catalytic converter, try this first because it will often clean them up, so they’ll pass the test.


I think that after performing these checkups, you won’t have any issue with passing the emission test. I always tell people to do a little bit of research before they do something. For example, if your car starts acting up and you take it to the mechanic right away, he will notice that you have no idea whats wrong with the car and will rip you off. Before you do that, always read something online, see some YouTube videos and try to get an idea of what might be wrong with your car, so if the mechanic starts to talk nonsense and tells you that you need to change a lot of parts, you will know if he is lying or not.

Now you can stop worrying about your car passing the emissions test, and do something about it.

Is your engine oil due for a change? Visit our Car Fluid Guide Website to learn the importance of changing your oil on time, which type of engine oil is best for your vehicle, and much more.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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