How to Test for a Clogged Catalytic Converter


The catalytic converter is subjected to reduced exhaust flow from the vehicle if the converter is allowed to overheat for any length of time. This is usually caused by poor spark plugs, sticking fuel injectors or a failure of sensors, causing the computer to richen the mixture to such a degree that there is a quantity of unburned fuel in the converter, causing it to burn the fuel and increase the heat.

Things You'll Need

  • Code scanner
  • Diagnosing the catalytic converter is necessary when the check engine light illuminates, and when cross-checked shows a failure. or the engine horsepower is drastically reduced.

  • Hook the scanner up to the port located under the driver's side of the dash. Turn the key to the run position with the engine off.

  • Push the "Read" button on the code scanner. Cross-reference the code with the code sheet provided with the scanner, which will provide an explanation of the code. If the code means that the catalytic converter is below the threshold, the converter is bad.

  • Check the converter for a blocked situation by feeling the amount of exhaust from the tail pipe. With the engine running, check the catalytic converter for overheating by its color. If it turns red, it is plugged. Listen for exhaust backing up and causing a hissing sound at the exhaust manifold.

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  • Don Bowman, A.S.E. Certified Mechanic
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