TechShop’s The Code Reader Podcast takes common DTCs, breaks down when and why they occur and looks at symptoms and causes to help listeners make an accurate diagnosis.
Listen to “P0420 – Catalyst System Efficiency Below Threshold” on Spreaker.
ASE certified technician and Managing Editor of TechShop Magazine, Eric Garbe discusses diagnostic trouble code P0420.
P0420 is stored when the readings of the pre- and post-cat oxygen sensors indicate that the catalytic converter is not working as efficiently as it should be in accordance with pre-programmed specifications.
Each catalytic convertor will have an oxygen sensor before it and after it. When the engine is warmed up and running in closed loop, the control unit monitors the reading of each sensor. Since the catalytic converter reduces the harmful emissions from the exhaust, when it is working properly, the readings between the two sensors will vary considerably. At a predetermined threshold of the sensor readings approaching similarity, the control unit interprets that the converter is not working efficiently and will store DTC P0420.
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