How to Diagnose Catalyst Efficiency Codes P0420 & P0430 with Confidence

In this episode of Around the Wheel, Motor Age technical and multimedia director Erik Screeden takes a deep dive into one of the most common and often misdiagnosed problems technicians face: catalyst efficiency codes P0420 and P0430. Many shops have experienced the frustration of replacing a catalytic converter only to see the check engine light return weeks later. As Screeden explains, these codes are not always straightforward, and without the right approach, they can lead to wasted time, unnecessary parts replacement, and a loss of customer trust. 

Using the Launch Tech USA X-431 Throttle V scan tool, Screeden demonstrates how technicians can go beyond basic DTCs and use the power of global OBD2 Mode-6 diagnostics. This mode allows access to the actual PCM test results used to determine catalyst efficiency, giving insight that most techs overlook. By combining this data with freeze frame information, oxygen sensor performance testing, and a full-system diagnostic scan, Screeden shows how to separate true converter failures from issues caused by fuel trim problems, vacuum leaks, or slow sensors. 

This video offers practical guidance to help technicians diagnose with confidence, avoid misdiagnosed trouble codes, and verify repairs effectively. Watch the full video to see how leveraging these tools can protect both your shop’s efficiency and your customers’ trust. For more information, visit https://www.launchtechusa.com/product-page/throttle-v.