Why do I have P0420 AND P0430?

Both cats failing together usually means something is damaging them — running rich, oil consumption, or coolant entering combustion.

Can I use aftermarket catalytic converters?

In many states, yes. In California, you must use CARB-compliant converters. Aftermarket cats are much cheaper than OEM.

Medium Severity

Emissions System

Same as P0420 but on bank 2. If both P0420 and P0430 are present, the issue may be systemic (engine running rich, etc.).

Common Fix

Replace cat bank 2 or fix root cause

Estimated Cost (DIY)

$100 - $1,500

Worn catalytic converter bank 2likely

Faulty downstream O2 sensor bank 2possible

Rich-running engine damaging both catspossible

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Why do I have P0420 AND P0430?: Both cats failing together usually means something is damaging them — running rich, oil consumption, or coolant entering combustion.
Can I use aftermarket catalytic converters?: In many states, yes. In California, you must use CARB-compliant converters. Aftermarket cats are much cheaper than OEM.

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