Is P0421 the same as P0420?

Very similar — P0421 specifically refers to the warm-up period. Same diagnostic approach.

How long do catalytic converters last?

Factory cats typically last 100,000-150,000 miles. Aftermarket cats may only last 30,000-80,000 miles.

Medium Severity

Emissions System

The bank 1 cat is not reaching efficiency during warm-up.

Common Fix

Replace cat or downstream O2

Estimated Cost (DIY)

$100 - $1,500

Aging catalytic converterlikely

Faulty O2 sensorpossible

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Is P0421 the same as P0420?: Very similar — P0421 specifically refers to the warm-up period. Same diagnostic approach.
How long do catalytic converters last?: Factory cats typically last 100,000-150,000 miles. Aftermarket cats may only last 30,000-80,000 miles.

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