p0421 DIY Diagnosis on an "00-"05 3g Mitsubishi eclipse 2.4 4g64.

[@clintonmcbeth3985]

This makes total sense!!! I have a 2001 Mitsubishi mirage and I’ve been struggling with this code for years I can’t believe I didn’t come across this concept sooner.

[@mitsubishikid1187]

It is often overlooked in diagnosing this code, and most of DIY car repair channels jump to the spark plug fouler spacer trick, as if it is a permemamt fix, in reality it can get you by, but in stricter smog states you could fail smog if they have a visual part of the test, if they see the spacers, so not a permanent option for all states, and what shop would suggest a $20-$80 fix when they can charge upwards of $300-$800+ on a brand new front catalytic converter, and the labor to install it, now in some cases the catalyst substrate could have separated inside the exhaust manifold, and in those cases a new catalytic converter is usally required to repair the car, and it's warrented, but if the car was always well maintained, it would make no sense that the catalytic converter would just warm up one morning and then decide to be bad for no reason lol, they are designed to last the life of the car, so long as it is running correctly, usually moisture seeps in to the oem welds on the manifold and when you start the car the temperature difference can cause micro-fractures, could also just be a defective front converter too, in some extreame cases the cracks will be visable and there could be indicaters showing where they are in the form of dark carbon tracing marks, just by looking at this manifold most techs would guess it's good but internally must be bad, but good machanics should not guess on customers cars they should know, and this fix has saved me $800 which is what i was quoted on a new converter back when i had this problem on my Galant, a few drill holes, grinding, and some welds, and the code was gone, it can work on any car honestly, and i hope it helps people save some money.

[@Styx_ia]

I have a 4G with a V6 and this helped a ton. Found out I had a major crack in my front exhaust manifold and had to buy a new cat. I appreciate the advice brother

[@mitsubishikid1187]

Thank you for following up, I'm glad the video helped and I'll consider sharing more tips like this in the future.

[@Diego-io9gj]

Did the weld work? Because i noticed bubbles and have to remove to get to the other side but i wanted to know if should weld it or just get a new catalytic converter

[@mitsubishikid1187]

@@Diego-io9gj yes it worked i had to remove the exhaust manifold/catalyst from the car if you live in a state other then CA or NY buying a new one is cheap enough that i'd go that route instead but if you inspect your old one look for a cracked or damaged catalyst substrate if it did not clog or break apart then welding the cracks shut is more then likely going to fix the problem.

[@LayZeeDawg]

3 am and i cant wait for daylight to try this out.

[@Crowlo17]

Did it work

[@LayZeeDawg]

​@Crowlo17 Sort of. Found no cracks, just a dead catalytic converter. Replaced it and code was gone.

[@Crowlo17]

@@LayZeeDawg dam but the catalytic converters are expensive here in Cali since they need to be oem approved

[@Crowlo17]

Does this work on a Mitsubishi eclipses 2006 base model?

[@Crowlo17]

4 cylinder

[@mitsubishikid1187]

@@Crowlo17 it works on all cars you can put a vacuum cleaner on blower setting, put it in the tailpipe and look for pre catalytic converter leaks if any are present they can cause a p0421 code most of the time they are seen on the headers.

[@bigbrown4455]

Are you able to clear codes with the reader in this video?

[@mitsubishikid1187]

It can but this particular code would come back after clearing codes and completing a drive cycle, a lot of people use the o2 sensor spark plug anti fouler spacer to trick the computer into not throwing a check engine light, and yes that can work, but after drilling and grinding/welding the cracks, seen at the end of the video, the code never came back on me.

[@kingedward93]

Thanks 👍👍👍👍👍👍👍

[@ashleyfite3964]

Would you know anything on a P1751 on a 2009 eclipse? I can’t find any answers

[@mitsubishikid1187]

That's usally a shift solenoid B issue, worst case scenario the transmission has to be taken apart to get to the shift solenoid part number MD758981 they are relatively cheap to purchase but expensive in labor to replace, the v6 and the 4 cylinder eclipse use the same part number, and they are inside the transmission on the valvebody it could be a wiring fault or the B solenoid is gummed up with trash, you can have a shop diagnose and test it though and that would definitively pin point the problem a bit more.

[@LiEazzyE]

So I have a 2007 Mitsubishi eclipse 2.4.L And I got the code p0431 and p0421 bank 1 and 2? Can u help me. I did the same test u did and put new exhaust gaskets on but my exhaust flange is leaking with the soap and water test. The bolts on there are tight. But the flange isn’t tight enough can that throw the code?

[@mitsubishikid1187]

You might have to use a brass wire wheel or brush to remove any old gasket material from the flange gasket sealing surface, sometimes old gasket material gets burned onto it, exhaust leaks can throw the codes it depends how bad the leak or leaks are, and where they are coming from, try to pinpoint exactly where it is that way you can focus efforts on correcting it , if you are using an old, or unknown condition or knockoff o2 sensors on the car that can also throw the catalyst codes, these cars tend to work best with the Oem denso o2 sensors, I do not recommend using cheap knockoff ebay or amazon etc o2 sensors, they are trash, if you can look inside the converters both upstream and down, make sure the catalyst substrate honeycomb inside the catalytic converter is still intact, and not rattling around, if that is the case then you definitely need a new catalytic converter, and you need to figure out what killed the old one, sometimes you can get away with welding or fixing leaks in the system, but other times your only option is just replacing the damaged parts, but if only one of them looks bad I would start with the worst looking one first, you also should do or have a leak down test performed on the car to figure out how well the piston rings and valves are sealing, if you pull the exhaust manifold off, look for oil in the exhaust ports and on the valves, sometimes the rings or valves will leak oil into the exhaust, common on vary high mileage engines, and that can kill a catalytic converter that or an improper air fuel ratio, and if something killed the converter you want to correct that before a new converter is installed to avoid damaging another one.

[@LiEazzyE]

I had got a new Cadillac converter on the car last month. And what if I change the Exhaust flange to get a new one? I got to do the test again I’ll let you know what happen?

[@LiEazzyE]

I think it’s my exhaust flange need to be changed

[@LiEazzyE]

I only got 1 code p0431 bank ?

[@ShakeelCarl]

By aspestus an make gasket for it