421 code where is the problem - 2000 Mitsubishi Galant

I don't think this should be in AC Cars category, makers of the AC Cobra car!

Just buy the right one for the unknown application

https://www.google.com/search?q=bosch+4202

$13.99 each. Don't mess with spark plugs.

https://www.google.com/search?q=ac+delco+41-421

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the p0421 code on this vehicle is either caused by a bad catalytic converter or an oxygen sensor. your mechanic has a scan tool that he can verify if the converter is faulty by comparing the rear o2 sensor to the front sensor. If the rear o2 sensor's voltage is switching from rich to lean (01-1.0v) similar to the front's, then, it's a bad converter. The rear o2 sensor should keep a steady voltage reading. Have him do this test while at cruising speeds. good luck

Hi there,

P0421 = Warm Up Catalyst Efficiency Below Threshold (Bank 1)

This means the HO2 (Oxygen) Sensor downstream of the catalytic converter on bank 1, is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

A code P0421 may mean that one or more of the following has happened: The catalytic converter is no longer functioning properly An oxygen sensor is not reading (functioning) properly A sparkplug is fouled up

Hi

Please check the link to get a detailed idea about the code:-

http://www.obd-codes.com/p0421

Please get back to us if you have further query else please accept the suggestion.
Thank you for contacting fixya.com

check oxygen sensors first

Your catalytic convertor is clogged you have to change before is damages ur o2 sensors

The Cat code could have cleared itself if the computer doesn't detect a problem anymore. Fix the EGR problem as it is still active.

Take it to AutoZone and have them scan the ECU for codes (it's free). Then post the codes here and we'll go from there.

djjfkg