Rick's Free Auto Repair Advice

Posts Tagged: 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

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


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