How to Diagnose Failing Catalytic Converter Using O2 Sensor Live Data | Oxygen Sensor Testing Guide

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Monitoring O2 sensor live data is one of the best ways to assess the condition of your catalytic converter. A properly functioning catalytic converter should show a steady upstream (pre-cat) O2 sensor signal fluctuating between 0.1V–0.9V, while the downstream (post-cat) O2 sensor should maintain a more stable voltage. If the downstream sensor mirrors the upstream sensor, it may indicate a failing catalytic converter. Using a diagnostic scanner, you can analyze O2 sensor voltages, response times, and fuel trim adjustments to determine whether your catalytic converter is working efficiently or if it needs replacement.