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Posts Tagged: 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

Toyota Scion P0420

Fix code P0420 Toyota Scion If you own a 4-cylinder Toyota or Scion vehicle and get a check engine light with trouble code P0420, welcome to the club. This has been a persistent problem with these vehicles. To get right to the point, the problem is bad software. Toyota has updated it. But that’s not all. If you don’t maintain this vehicle EXACTLY as Toyota says, you can accelerate this problem. It all starts with misfires and not changing your oil. Misfires send unburned fuel down into the catalytic converter where it’s … Read More

P0420 P0421 P0422 P0423 P0424 P0430 P0431 P0432 P0433 P0434

Fix code P0420 P0421 P0422 P0423 P0424 P0430 P0431 P0432 P0433 P0434 Some blog readers have been asking if they really have to replace a $1,200 catalytic converter just because they’re seeing these codes. Perhaps not. But before I dig into what may be causing the problem, let’s do a quick explanation of exactly what a catalytic converter does and how it may fail. Inside the catalytic converter you’ll find a honeycomb coated with rare-earth metals like Rhodium, cerium, platinum, and palladium. These metals react with oxygen, fuel, oil, to … 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

P0420 after Catalytic Converter Replacement

Why do I get P0420 after Catalytic Converter Replacement Trouble Code P0420 is “Catalyst System Efficiency Below Threshold.” This coded sets if the computer see similar readings from both the pre- and post- converter oxy gen sensors. The pre-cat sensor should switch rich/lean. But the post-cat sensor should give a fairly steady reading, indicating that the converter is doing it’s job. Independent repair shops report that the majority of these P0420 codes after converter replacement are due to the installation of AFTERMARKET converters. They’re less expensive than original equipment, well, … Read More


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