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Posts Tagged: Code P0420

Fix Code P0420

Fix Code P0420 A P0420 code means your catalytic converter has failed an efficiency test. In other words, it’s not removing harmful combustion byproducts from the exhaust. Many people think that the way to fix code P0420 is to replace the oxygen sensors. That’s wrong. In fact, the vehicle comuter can’t even come to the conclusion that your catalytic converter has failed the efficiency test if your oxygen sensors are bad. So don’t waste your time and money on oxygen sensors. What goes wrong with a cat converter? Catalytic converters … 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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