Catalytic Converter Systems

Catalytic Converters

Almost every vehicle on the road today has a catalytic converter. This is an essential part of emissions reduction in today's vehicles. The catalytic converter takes the exhaust gases that come into your exhaust from the combustion process and converts them to gases that pollute the atmosphere significantly less. Many vehicles have plenty of fuel that was not burned in the combustion process. By passing those gasses through the catalytic converter they are reduced and altered in a manner that is less of a pollutant to the atmosphere.

A three-way catalytic converter has three simultaneous tasks:

  1. Reduction of nitrogen oxides to nitrogen and oxygen
  2. Oxidation of carbon monoxide to carbon dioxide
  3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water

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For a good video on what a catalytic converter is, what it looks like and general operation, check out this youtube video.

Every vehicle varies, but all cars manufactured after 1975 have at least one catalytic converter. For smaller engines found in most cars you will find one catalytic converter per engine bank. Four cylinder engines can sometimes be referred to in technical documents as having two banks, but due to their exhaust flow they are generally considered to be one bank when taking converters into account.

How do I know if my catalytic converter is bad?

When I replace my catalytic converter, what other items should I be pay attention to?

What can cause my catalytic converter to go bad?

How do I know if my catalytic converter is bad?

Catalytic converters can do or exhibit several symptoms to indicate that they are not functioning as they should. Here are a few of the ways to tell that you may have a catalytic converter going bad.

  • The first thing people may notice is that their exhaust smell may be much stronger than it has ever been.
  • There are also instances where the catalytic converter will become like a brick within its shell and you will hear excessive rattling coming from the exhaust system. In this instance it may start to break up and flow through the exhaust system and blowing through the muffler or it can also clog the muffler.
  • The check engine light may come on with the codes P0420 and/or P0430.
  • Excessive oil consumption will lead to permanent damage the catalytic converter. IE: If your car oil is regularly low and you can't find or see an obvious leak, it is likely your engine is consuming the oil.

Please note that the list outlined above are symptoms of a converter that may be going bad but it does not mean that your catalytic converter is going bad if those symptoms are there. There are ways that professionals can check to see if your catalytic converter is deteriorated/deteriorating.


When I replace my catalytic converter, what other items should I be pay attention to?

Underlying Engine Issues

When replacing a catalytic converter you should be aware that some manufacturers have very fine line details included with their warranty. Since most catalytic converters actually go bad from engine related issues, it is wise to resolve the original problem. This will prevent your warranty from being voided with the manufacturer of the aftermarket catalytic converter. Issues can include but not be limited to: mass air flow sensor, leaking intake manifolds, leaking fuel injectors, improper fuel pressure, excessive oil consumption, malfunctioning oxygen sensors and/or fuel ratio sensors.

Oxygen Sensors

If you replace the catalytic converter system within your vehicle, we can't stress this next step enough... REPLACE ALL Oxygen Sensors. Oxygen sensors are what monitors the exhaust gasses coming from the exhaust manifold and indicates the pattern to the engine computer. The engine computer is then specifically calibrated to respond to the data from the oxygen sensors and adjust the fuel mixture accordingly. If the oxygen sensors are transmitting improper information to the ECM/PCM, the computer will then respond to the incorrect data and cause damage over time.

Air/Fuel Ratio Sensors

The Air/Fuel Ratio Sensor is a more sophisticated version of the oxygen sensor. The sensor essentially performs the same functions as the original oxygen sensors as well as a more accurate monitor of unburned fuel in the exhaust gasses. These sensors are typically much more expensive than standard oxygen sensors but their replacement is essential.

It was once relayed to us that if vehicle owners would replace their oxygen sensors every 80,000 miles and keep up with vehicle maintenance, catalytic converter manufacturers wouldn't be in need for the aftermarket automotive ecosystem. This was told to us by a reputable catalytic converter shop that we do business with. We take those comments seriously and bring that knowledge and much more to the table when we consult with customers regarding maintenance that is pertinent to their vehicle.


What can cause my catalytic converter to go bad?

Catalytic converters rarely go bad on their own. While it is very possible it's not always likely. Usually there is an underlying problem with the vehicle that will lead to premature wear in the catalytic converter.

Here are some of the items that can lead to premature wear of your catalytic converter:

  • Oxygen sensors that are not performing as intended
  • Excessive carbon in the engine
  • Engine consuming excessive amounts of oil through piston rings
  • Improper fuel pressure

At Joman Auto Service we sell and install catalytic converters from a variety of manufacturers but have a working relationship with Walker Exhaust. Click here to learn about our special with Walker Direct Fit Catalytic Converters from 9/1/2014 till 10/31/2014.


Click here to schedule an appointment to have your vehicle evaluated for what you may need.