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2002 Chevrolet Suburban P0420 Code Still Present After Catalytic Converter Replacement

Model: 2002 Chevy Suburban Fault Code: P0420 Posted: 2012-03-20 22:44

We own a 2002 Chevrolet Suburban 1500 that we purchased used about a year ago. The vehicle recently triggered a P0420 and P0420PD diagnostic trouble code (DTC). Initially, the engine would idle roughly on cold mornings. We replaced the exhaust gasket, which improved the idle but did not resolve the code. After being advised to replace the catalytic converter, we installed a new one a few days ago. While the P0420PD code cleared, the P0420 code remains active. We are preparing for a long road trip to Mexico and want to ensure the vehicle is in good condition—especially regarding emissions-related issues. We've already completed routine maintenance: coolant replacement, fuel filter change, oil change, and a transmission flush (which was necessary). The only remaining component we're considering replacing are the oxygen sensors, which cost $100 each. However, there are no specific error codes indicating a faulty oxygen sensor, as such issues typically trigger a distinct DTC. The question is: should we replace the oxygen sensors or focus on resolving the P0420 code? Given our spending so far (and the fact that labor was only incurred for the catalytic converter replacement due to welding), any expert advice would be greatly appreciated. The vehicle runs smoothly with no performance issues—only this persistent DTC is causing stress. Note: This issue may relate to a failing or improperly installed catalytic converter, as P0420 indicates insufficient exhaust gas conversion efficiency.

Related fault codes
P0420
Comments (3)
Anonymous 2012-03-21 05:08

Do not replace the catalytic converter before your trip. Oxygen sensors do not resolve a P0420 code and will not clear it on their own. To fix this issue, you must install a high-quality, OEM-style catalytic converter—universal fits are not recommended. A properly functioning converter is essential for passing emissions tests and clearing the P0420 DTC.

Anonymous 2012-03-21 18:16

I'm glad to hear you cleared the code last night—it's reassuring! However, I should note that if the catalyst monitor fails, the vehicle will fail smog inspections. The absence of a specific oxygen sensor code suggests it may not be the root cause. It’s possible the new converter needs time to stabilize and register properly in the system. Monitor the code over the next few days; if it returns, further diagnostics are needed.

Anonymous 2012-03-21 19:20

Correct—without a successful catalyst monitor pass, the vehicle will fail emissions testing. The issue won’t resolve on its own and may only worsen. You need an OEM-quality catalytic converter for reliable performance. Walker converters are known to offer excellent direct-fit options and are highly recommended for this model year.