Signs of a bad catalytic converter

Written by ronni dee
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Signs of a bad catalytic converter
A few key symptoms let you know if your catalytic converter is bad. (muscle car image by patrimonio designs from

Diagnosing a mechanical problem with a vehicle can be tough, especially diagnosing it down to the exact part. Determining if your catalytic converter is the culprit is no exception, because most of the symptoms are also symptoms of many other mechanical issues. However, a few key symptoms point directly to the catalytic converter.

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A foul smell is the most common sign of a bad catalytic converter. If you smell what seems to be a rotten egg and it gets stronger over time, the catalytic converter is not working properly.

Fuel Economy

A large drop in your fuel economy may be a sign that your catalytic converter is going bad or is blocked.


A lack of power, especially at high speeds, may be a sign that the catalytic converter is going, or has gone, bad.


A vehicle that stalls during idle, or idles rough, may have a blocked or bad catalytic converter.


Your catalytic converter may be blocked if you experience bucking or hesitation while trying to accelerate. Additionally, your vehicle may run at a higher than normal temperature.


A catalytic converter typically doesn't go bad without an underlying cause. A mechanic should be able to find the original problem and may not have to replace the converter.

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