Catalytic Converter Tech Tips

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Common Symptoms of a Failed or Failing Catalytic Converter

  • The vehicle may have reduced power. As you increase pressure on the throttle, the vehicle does not go any faster and the engine does not increase rpms. This may indicate a plugged converter.
  • You may hear an annoying rattle from the exhaust, and in particular from the converter area. This may be caused by the internal substrates inside the catalytic converter falling apart.
  • The vehicle may fail emissions. This can be caused by a catalytic converter that has fallen apart internally, or a catalytic converter that has been gutted for one reason of the other.
  • The vehicle may make a loud air rushing noise from areas of the exhaust in front of the converter. This may indicate a plugged converter that is forcing the excess pressure through leaks in the exhaust system.
  • The vehicle’s check engine light may be coming on. This may be due to a converter failure and the O2 sensors are picking up on the abnormality and signaling you through the instrument panel warning light.
  • The vehicle is getting poor fuel mileage. A faulty catalytic converter will cause the engine to perform at less than peak performance to terribly. This lack of performance results in poor fuel mileage.

A vehicle with a failed or failing catalytic converter may exhibit some or all of the above symptoms.

Common Simple Diagnosis Of a Catalytic Converter Failure

Most catalytic converter failures should be diagnosed by a professional , but there are some things the Do It Yourselfers can do themselves to make this determination with reasonable confidence. When performing any repairs to a vehicle, always take all safety precautions necessary to avoid injury. Refer to the owner’s manual, repair manuals, etc.

If you feel the converter may be plugged:

You can loosen the exhaust in front of the converter and start the engine. If there is a considerable change in responsiveness and power, the converter may be plugged and should be replaced. Please note that it is unlawful to operate a vehicle that requires a catalytic converter without the catalytic converter or bypassing the catalytic converter.

You can remove the front oxygen sensor and install a pressure gage. If excessive exhaust pressure is found, that would indicate a plugged converter and the resulting back pressure that causes the high pressure reading. Refer to a repair manual for exhaust backpressure specs.

If you feel the converter has an internal failure.

Make sure the converter has cooled to the touch. Bang on the converter with your hand or a rubber mallet. If you hear items loose inside of it, the catalytic converter needs to be replaced.

Remove the pipe directly behind the catalytic converter and look inside for loose pieces of substrate. If you see loose pieces, the converter needs to be replaced. Take the vehicle to an emission testing center and have them perform an emission test. They will be happy to tell you if the catalytic converter is not functioning properly. Make sure the vehicle is at full operating temperature before having it tested.