How to Fix a Car Emission Problem

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Automobile emissions standards are specific limits set on the amount of pollutants that can be released into the environment. There are both federal standards and state requirements. California, for example, has its own set of stringent laws which are often followed by other states. If you have an emission problem, you need to check your state's requirements and then find an authorised centre to get an official emissions test. There are dozens of possible fixes to the problem, depending on the exact cause of the emission trouble.

Skill level:
Moderately Easy

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  1. 1

    Determine if the problem is illegal. A car can have an emission problem but it might still be all right to drive, depending on the exact issue. Take your vehicle to an authorised emissions tester to determine if the problem is allowable by law. A list of authorised test centres can be found on your state's department of motor vehicles website. A list of the various standards can be found at

  2. 2

    Determine the exact emission problem. Emission problems come from many sources. An authorised mechanic will provide a copy of the test results for your vehicle. An emissions test measures the amount of specific pollutants and compounds coming out of your tailpipe. These pollutants include carbon monoxide, nitrous oxide and hydrocarbons. Your emissions test results will show which of these levels exceed the legal limits.

  3. 3

    Diagnose the source of the bad emissions. Bad emissions can have many sources. Excessive levels of carbon monoxide are caused by incomplete combustion. According to, this can be caused by a number of things including a dirty air filter, a faulty oxygen sensor, a defective manifold sensor, a defective throttle position sensor or a defective engine coolant temperature sensor. The website also lists myriad other problems that could result in excess levels of the other pollutants.

    Excessive nitrous oxide levels can be the result of a defective exhaust gas recirculation system, a faulty catalytic converter, engine overheating or high engine mileage. Excessive hydrocarbons can be the results of improper ignition timing, defective ignition components or a faulty fuel mixture.

    Fixing any of these problems starts with a proper reading of the emissions test and replacement or repair of the faulty part.

  4. 4

    Determine if there is tailpipe smoke. Check to see if there is actual smoke coming out of your car's tailpipe. The colour of the smoke can possibly tell you the source of the problem.

    White or blue smoke indicates that oil is getting through the valve seals into the combustion chambers. Replacing the seals should fix the problem. Black smoke, often found with older cars, is usually caused by air getting into the fuel mixture of your engine. A tune-up could possibly fix this but it might be a problem with the engine. Even a proper diagnosis for this could be expensive. Pure white smoke indicates that either coolant or transmission fluid is leaking into the combustion chambers. It might be the result of a leaky vacuum tube or head gasket which would need to be replaced.

  5. 5

    Fix the problem. Whether you plan to do it yourself or take your vehicle to a mechanic, proper diagnosis of the source of the emissions problem is the key to solving it. Use the emission test results as your base for any repairs. If you take the car to a mechanic, make sure his repair recommendations match up with the numbers on the emissions results.

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