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What Caused the Catalytic Converter Failure

In my previous article I may of guilted you into vowing to repair your vehicle so your check engine light is not on. Remember this light is on when your vehicle is typically not at its best, environmentally speaking.

One very common fault discussed was a malfunctioning catalytic converter. The catalytic converter, located in your exhaust system, cleans up the inefficiencies of the internal combustion engine.

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As the catalytic converter relies on precious metals like platinum, palladium, rhodium and cesium to act as catalysts in the chemical process of converting the pollutants; unburned hydrocarbons, carbon monoxide, and nitrous oxides into carbon dioxide, water, nitrogen and oxygen it may be obvious that these units are expensive. Your vehicle may have more than one of these as well.

True to a chemical reaction involving a catalyst, the catalyst materials (in this case precious metals) are not consumed. Essentially then a catalytic converter can last indefinitely provided it is cared for properly. The outside of a converter is stainless steel and is relatively immune to corrosion. In many cases the converter will be shielded with more stainless steel to help hold the heat in. The inside is typically a honeycomb ceramic that provides a huge surface area for the exhaust to travel through. The honeycomb is coated (or washed) in precious metals.

As one can imagine the converter can be damaged by impact. Any outside damage that distorts the inner wall of the converter can crack the honeycomb substrate. Once broken the path through the honeycomb can become blocked and eventually reduce or totally plug the exhaust system. A hard to ignore extreme lack of power will be the symptom that forces a repair.

The more common catalytic converter failure is the result of poor maintenance and repair practices. If your vehicle ever developed a problem where the check engine light was flashing and you continued driving for some time like that you likely will end up having more than one thing to fix. A flashing check engine light is generally the result of misfire. Misfire is when the spark plug does not ignite the air fuel mixture in one or more cylinders. Along with reducing your engine’s power the fuel that is not ignited in the cylinder to make power flows into the catalytic converter. The catalytic converter, being a furnace of sorts will burn that extra fuel but may, in the process, become too hot. Too hot means the honeycomb substrate will start to melt. Again, melted substrate reduces exhaust gas flow and messes up the surface area of the precious metals. The result is reduced catalytic function.

The previous scenarios are both readily apparent to the driver of a vehicle. If something hits the underside of your vehicle make sure you have it inspected. If you have the proper insurance a “rock on road” damaged converter can be claimed and repaired. If your check engine light is flashing stop driving as soon as it is safe to do so.

Another scenario is having to replace your converter due to more subtle neglected repairs and maintenance. Driving around with the check engine light on is most common. If your check engine light is on, your vehicle is operating at a less than optimum state. In many cases the life of your catalytic converter/s will be affected by this. Extra lean or rich air fuel mixtures will overwork the catalyst.

At the shop these vehicles come in with a check light on. The light may be on because of a faulty oxygen sensor or mass air flow sensor. With these ongoing faults the state of the catalytic converter cannot be tested by the onboard diagnostic system. The owner decides it is time to figure out what has been keeping that check engine light on for the last six months. The technician replaces the bad oxygen sensor and gives the vehicle back to the customer. Not more than a few days later the vehicle is back and the customer is unhappy. The check engine light is back on again.

Guess what? The new oxygen sensor now allowed the diagnostic system to test the catalytic converter that it had to neglect for the past six months. The second bill is bigger than the first but the second could have been totally eliminated by fixing that check engine light as soon as it came on.

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