Catalytic Converter (CAT) Failure Symptoms and Precautions

Catalytic Converter

In most of the countries emission control laws are not enforced by the governments. Because of which the residents of such countries are not aware of the importance of Catalytic Converters in their automobiles. However, the awareness level has improved a little, with the recent trend of JDM imported vehicles (Japanese Domestic Motors). In this blog i aim to make the reader aware of the “Catalytic Converter (CAT) Failure Symptoms and Precautions” to enhance awareness of the vehicle owners and to improve the useful life of the Catalytic Converters. In this article, I’ll discuss following aspects of Catalytic Converters:-

  1. Purpose of Catalytic Converter
  2. Construction of Catalytic Converter
  3. Causes of Catalytic Converter Failure
  4. Symptoms of Catalytic Converter Failure
  5. Precautions and Care for Catalytic Converter


Purpose of Catalytic Converter

The purpose of catalytic Converter is to treat the combustion gases caused by the internal combustion engines, to make them environment friendly before disposing-off into the environment. Catalytic Converter is installed after the exhaust manifold and before the Silencer muffler. Catalytic Converter is designed in such a way that the exhaust gases undergo chemical reaction in it and forms harmless Carbon dioxide and water.

Construction of Catalytic Converter

There are two types of Catalytic Converters in use now a days. The construction of both are different but the purpose and functioning principle remains the same i.e in both the types the exhaust gases are subjected to chemical reaction which make them environment friendly. The two types are “Pelletized” and the “Monolithic Honeycomb” construction. In both types the base material is Ceramic.

In Pelletized design, thousands of tiny pellets are put together in a container in such a way that the exhaust gases may easily pass through them and get treated. On the other hand, in Monolithic Honeycomb design, Catalytic Converter is one piece of ceramic which has multiple longitudinal passages through which exhaust gases pass and get treated. This design is called honeycomb because the cross-section forms a honeycomb structure. In both the designs, the ceramic pellets and the honeycomb are coated with precious metals (platinum, paladium or rhodium) which reacts with the exhaust gases and forms Carbon Dioxide, Nitrogen and Water, which are not detrimental to the environment.

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Causes of Catalytic Converter Failure

The Catalytic Converter fails to perform the desired function due to two reasons:

  1. Either the Catalytic Converter gets clogged due to carbon and lead deposits, which primarily results due to poor quality of fuel used. If leaded fuel is used for extended period of time the Catalytic Converter will fail to perform its desired function, and it is expected that vehicle will fail the emission test.
  2. Other reason could be the damage to the metal coating (platinum, paladium or rhodium), which is an irreparable damage. This type of damage is caused when an un-burnt fuel reaches the catalytic converter. Un-burnt fuel in exhaust gases could be the outcome of mis-tuned engine, incorrect engine timing, fouled / contaminated spark plugs, faulty / contaminated Exhaust Gas Regulator (EGR), faulty fuel injectors etc. So, when un-burnt fuel enters the already-hot converter, ignites and makes the Catalytic Converter red hot and may cause melting/deformation, which is an undesired condition for CAT.  Such a high temperature damage the coating of the converter making it permanently un-usable.

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Symptoms of Catalytic Converter Failure

Failed Catalytic Converter may show following symptoms:-

    1. Check Engine Light (CEL) with OBD-II code P0420. This code could be observed either due to Catalytic Converter not operating at maximum efficiency or even if there is a problem with O2 (oxygen) sensors.
    2. Smelly exhaust gases, like “Rotten Egg” or sometime that of un-burnt fuel, even after reaching optimum engine temperatures. During cold engine start i.e usually first start in the morning, mild smell in exhaust is considered normal, sooner the engine reaches its operating temperature, the CAT becomes effective, the smell should stop.
    3. Relatively higher fuel consumption i.e MPG drops (Mileage per Gallon).
    4. Low engine power may be observed if the Catalytic Converter gets clogged due to carbon / lead deposits.
    5. Sometimes the failure of Converter cannot be detected during routine vehicle running. In such cases the failure can only be found during emission test. It is always advisable to have a pre-emission check before going for the actual test.
    6. In case of severe physical damage to the Catalytic Converter, rattling noise may also be observed during engine idling.

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Precautions and Care for Catalytic Converter

Enhance service life of Catalytic Converters by keeping in mind below listed points and precautions:-

  1. Use only unleaded gasoline.
  2. Avoid prolonged idling of engine (not more than 15-20 min), especially during hot weather with air-conditioning ON.
  3. Avoid Coasting with engine turned off.
  4. Be careful not to let a large amount of un-burned gasoline enter the converter.
  5. Exercise caution for hot metal when working on Catalytic Converter.
  6. Conduct a spark jump test only when its essentially required. Make it as short as possible, and do not open the
  7. Conduct engine compression checks within the shortest possible time.
  8. Avoid situations which can result in engine misfire (e.g. starting the engine when the fuel tank is
    nearly empty.)
  9. Dispose-off removed Catalytic Converter properly. Fuel/Oil contaminated converters are fire hazards.

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