Review the 'Possible Causes' mentioned above and visually examine the corresponding wiring harness and connectors. Ensure to check for any damaged components and inspect the connector pins for signs of being broken, bent, pushed out, or corroded.
As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (it is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases, the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.
To diagnose the P0420 Chevrolet code, it typically requires 1.0 hour of labor. The specific diagnosis time and labor rates at auto repair shops can differ based on factors such as the location, make and model of the vehicle, and even the engine type. It is common for most auto repair shops to charge between $75 and $150 per hour.
A 3-way catalyst controls emissions of hydrocarbons, Carbon Monoxide (CO), and Nitrogen Oxide (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbons and the CO that are present in the exhaust gas. This process converts the hydrocarbons and the CO into water vapor and carbon dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalyst also stores oxygen. The Engine Control Module (ECM) monitors this process by using Heated Oxygen Sensors (HO2S) that are in the exhaust stream before and after the 3- way catalyst. The HO2S produces an output signal that the ECM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emissions efficiently. The ECM monitors the efficiency of the catalyst by monitoring the HO2S during an off-idle, Decel Fuel Cut-Off (DFCO) event. When the catalyst is functioning properly, the post-catalyst HO2S response to the fuel conditions during the DFCO event is slow compared to the response of the pre-catalyst HO2S. When the post-HO2S response is near that of the pre-HO2S, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold. The Diagnostic Trouble Code (DTC) will be set when the ECM determines that the efficiency of the catalyst has degraded below a calibrated threshold.
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