Before you drive to the gas station, you might want to check your fuel filter first. A malfunctioning fuel filter can allow contaminants and sediment into the engine, which will lower your catalyst efficiency below threshold. Another likely cause of a low catalyst efficiency is a clogged oxygen sensor that may be incorrectly reading the exhaust fumes as normal levels of oxygen. If this is happening, then it's time for an oxygen sensor replacement. A clogged catalytic converter will also lower your catalyst system efficiency below threshold, so it's important to look at both the exhaust and intake air flow when diagnosing a faulty converter.
Failing spark plugs will result in lower catalyst efficiencies too.
https://autovehicleparts.com/h....ow-to-fix-catalyst-s
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