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Wayne Crawford
Wayne Crawford, Shop Owner
Category: Mitsubishi
Satisfied Customers: 4017
Experience:  General Repair Shop Owner
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I'm having a constant problem with code p0421 2003 montero

Customer Question

I'm having a constant problem with code p0421 2003 montero sport 3.0 v6.
i have replaced the large cat in the back but the code is still there so i guess the small ones in the front are bad?
Which one?
Can they be taken off and cleaned up?
Would that work?
Thank you for any advise.
Submitted: 2 years ago.
Category: Mitsubishi
Expert:  Wayne Crawford replied 2 years ago.
Hello. My name is ***** ***** I will be helping you today.This code indicates that the front cat on the passenger side is bad. In some rarer cases it is a bad oxygen sensor but its usually the catalytic converter.You cannot clean it.. the code is not for it being dirty its just not doing its job very well anymore. Its worn out basically.As a side note I have had terrible luck trying to use aftermarket cats on these. I will only install an OEM part because most of the aftermarkets I have tried end up setting a code. Just so you know that ahead of time.