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Posts Tagged: Code P0420

How to fix Code P0420

What is code P0420 Catalyst System Efficiency Below Threshold When attach a trouble code reader and come up with a P0420, your first assumption may be that you need a new catalytic converter, simply because the words catalytic converter are mentioned in the code. After the tests you may indeed discover that the catalytic converter is bad. But first you have to understand how the air/fuel and emissions systems work. How the air and fuel mixtures are calculated The powertrain control module (PCM) receives inputs from the engine coolant temp … Read More

P0420 Catalyst System Efficiency

P0420 Catalyst System Efficiency Below Threshold (Bank 1) This code means the catalytic converter that treats the exhaust for Bank 1 has failed it’s testing. The oxygen sensor in front of the catalytic converter switches back and forth between rich and lean as the computer constantly changes air fuel mixture. But after the exhaust leaves the converter, the next oxygen sensor should not switch between rich and lean. If it does, that means the catalytic converter is NOT doing its job. Catalytic converters generally do NOT fail on their own. … Read More


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