Warm Up Catalytic Converter Efficiency Below Threshold

Reply Subscribe

Thread Tools

Search this Thread

May 4, 2023 | 02:36 PM

#31

Truwarrior22

Thread Starter

Senior Member

Joined: Mar 2016

Posts: 174

Quote:

Originally Posted by MalcNZ

Ouch, so if I read it right. You have had to replace the Cat on the header manifold. So on my V6 I am possibly up for 2 cats (1 per cylinder bank) and then possibly the main cat as well. That will work out at major dollars as here in NZ the only choice is Genuine from Mitsi or import generics from overseas which will include extra freight costs.

I had code 421. I guess that’s the warm up catalytic converter, ie manifold. Appears no one actually had a clogged catalytic converter yet. Mine check engine light would just go on and off intermittently without any performance issues. If you have emissions testing, a bottle of cataclean may help but likely temporarily.

Jan 20, 2026 | 08:48 PM

#32

Rio5

Junior Member

Joined: Jan 2026

Posts: 1

Sorry for digging up this thread. So the only solution for P0421 intermittent is to change the cat converter? My 2016 112k miles is having this issue.

Jan 21, 2026 | 07:51 AM

#33

Galantralliart09

Junior Member

Joined: Feb 2021

Posts: 9

Quote:

Originally Posted by Rio5

Sorry for digging up this thread. So the only solution for P0421 intermittent is to change the cat converter? My 2016 112k miles is having this issue.

Yes, it's the only solution for that code. On my outlander it went out at almost 70k miles.