P0420: Catalyst System Efficiency Below Threshold (Bank 1)

Last Updated on April 18, 2020 by themechanic

The internal combustion engine of your automobile produces a lot of dangerous pollutants as a result of the combustion process. Car manufacturers are required to help protect the environment by coming up with ways to reduce the toxicity of these pollutants before they’re released outside. That is why the catalytic converter was invented. It breaks down the toxicity level of these dangerous pollutants and makes them less harmful to the atmosphere.

If there ever comes a time when your catalytic converter stops working properly, the pollutants released from your vehicle will become more harmful than normal. You won’t even realize your catalytic converter has gone bad until you experience certain symptoms, such as a rotten egg smell, poor fuel economy, weak engine power, and the illumination of the “Check Engine” light on your dashboard.

Once you experience these symptoms, run a diagnostic check on your vehicle. If the catalytic converter truly has gone bad, then diagnostic trouble code P0420 will appear on the display screen. The official definition of P0420 is “Catalyst System Efficiency Below Threshold (Bank 1).” This basically indicates that your catalytic converter is less efficient than normal. The likely reason for this is that it has gone bad.

You should not wait to have your catalytic converter replaced. Even though you can still drive your vehicle around, it could pose a threat to other drivers on the road because of the weak acceleration and power coming from the engine. You must have the catalytic converter replaced if you want to restore the acceleration back to normal.

Since P0420 only refers to an inefficient catalytic converter, it doesn’t necessarily mean the catalytic converter is bad. There are other things which can affect the functionality of the catalytic converter, such as a bad oxygen sensor, bad air-fuel sensor, exhaust system leak, engine misfire, abnormal air-to-fuel ratio, and leaded gasoline.

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You’ll know for sure which specific component is causing the problem because other codes will show up on the screen alongside this one. You might see misfire codes like P0300 or P0303, or engine lean or rich codes like P0174 or P0171. Again, an auto technician is best equipped to use this information for an accurate diagnosis.

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