how i fixed my F***ing 420 code

[shin]

well i am new here... and i decide to join you guys in this forum since it seems to have the most traffic and nice set up... but anyways just picked up my first suby its a 98 legacy gt wagon... and i will say i love it... fell in love with it on the test drive... and the cel was on when i got it and i have the guy check it and it said it was 0420 catalyst below threshold bs and what not.. so he cleared it and i bought it and within about 100 miles came back on.... changed the front o2 sensor and cleared it and again 100 miles later same thing... so after many many more hours of research and a call to the dealer i was convinced i had a bad cat... and since i read a lot saying its a good idea to replace both and then both o2 sensors witch runs about $600 in parts.... and it being my beater i decided ill pass... and make my own way at fixing it... this will not work for you if you have to pass smog...or you are a emissions hippy...sorry i dont have pictures so i will try my best to type my pictures into words ...i first started out by pulling the front cat down... witch contains 1 o2 sensor... and if you notice it is at the front of the cat before the material... so i then went and cut open the cat but cutting it if i were to cut a square out of it but i only made three cuts... and then i bent it back and opened it like a door.... then i took a big flat head screwdriver and a hammer and beat the material out.. when you do this make sure you remove all of it... there is a wirey mesh that wraps around it and also two rings on the ends that have to be removed or it will rattle/ end up in the other cat... and once i had everything removed,i then took a piece of small angle iron that i had laying around.. and put it around the o2 so it would catch air and slow the flow across it... as in the V was on the back side of it... and welded it in there. i am sure if you just got a piece of pipe a little bigger then the o2 and welded in there it would work two... and and then when that was done i bent the cat door shut and welded it up and reinstalled it with new gaskets... and now i have almost 300 miles on it and no light... money spent nada money saved >=$600 jsut thought i would chime in to help save people some money... enjoy and do at your own risk... sorry again for no pics

[WoodsWagon]

Instead of all that work you could have just got a 21mm thread flat washer spark plug anti-fouler from your local Help! parts aisle, drilled it out with a 1/2" bit, threaded the rear O2 sensor into it, and then threaded that into the exhaust. It spaces the sensor back out of the exhaust, gets rid of the 420 code, even with no cat. And I believe the pack of 2 antifoulers costs $3, so that's a buck fifty per car you fix.

[GeneralDisorder]

Hope you didn't put that flow restrictor on the front O2.......

 

Yeah that's way overkill and too much work. Spacer on the rear O2 is all you need. I've done half a dozen of them.~$5.

 

Research fail......

 

GD

[shin]

no i put the flow restricter behind the o2... and as far as the spark plug anti fouler trick, witch i read a lot of... that would not help in a plugged cat case.. plus i preffer not to run cats...i like my higher flowing exhaust... and it was about a hours worth of time... i was just going to go get a test pipe bent up but this works just as good.. and again this is how i fixed it just another way.... thats all plus you would also gain a higher flow exhaust..

[Fairtax4me]

These cars rarely have plugged cats. And quite often even if the whole system is replaced,even with brand new Subaru parts, it still doesn't get rid of the code.

 

Props for DIY ingenuity!

But there are cheaper and easier ways to do the same thing if you just do some reading.

 

As for restricting flow around the front O2 sensor. That's a problem. The front O2 sensor adjusts fuel mixture, so preventing exhaust from flowing across it can cause performance issues. Bad fuel mileage, driveability problems, etc.

Put your blocker on the rear O2 sensor, because that's the one that checks the efficiency of the cat.

Edited November 26, 2010 by Fairtax4me

[shin]

These cars rarely have plugged cats. And quite often even if the whole system is replaced,even with brand new Subaru parts, it still doesn't get rid of the code.

 

Props for DIY ingenuity!

But there are cheaper and easier ways to do the same thing if you just do some reading.

 

As for restricting flow around the front O2 sensor. That's a problem. The front O2 sensor adjusts fuel mixture, so preventing exhaust from flowing across it can cause performance issues. Bad fuel mileage, driveability problems, etc.

Put your blocker on the rear O2 sensor, because that's the one that checks the efficiency of the cat.

 

see first i did buy a new front cat and i noticed that were the o2 does go they pretty much have a shield around it.. its just a piece of oversized pipe... it was a walker brand cat.. so wouldnt that be just as bad as what i did... if the rear o2 sensor checks the efficency of the cat then how come the 420 code went away while messing with the front one.. and wouldnt doing the spark plug fouler trick restrict flow across the o2 just as much if not worse since you are pulling it out of the cat? if this sounds cocky it was not intended, one of the downfalls of writing over the web...

[brus brother]

Don't worry Shin. Welcome to the board. I've learned a thing or two (that's an understatement) from the members here.

As the saying goes, there's more than one way to skin a cat. In this case, perhaps what others are pointing out is that you used a chainsaw to do the skinning.

Glad it worked for you so far but keep an eye out down the road for the possible pitfalls suggested in your method.

[idosubaru]

you did it a different way and fixed it, awesome.

 

the rear O2 sensor doesn't affect performance. so there's no issue with tweaking it as it doesn't affect anything. it's output is only compared to the front's, it isn't used by the ECU as such so it doesn't affect performance, gas mileage, etc.

 

while the rear is super easy, i even buy the part off ebay instead of making it myself, who cares. if the code is gone i doubt you'll see any real world significance either way.

[Fairtax4me]

if the rear o2 sensor checks the efficency of the cat then how come the 420 code went away while messing with the front one..

 

The reason for blocking the rear sensor is that the ECU looks for a change in voltage at the rear sensor compared to the front sensor. The change in voltage is reflective of the change in oxygen content in the exhaust after the catalytic converter does it's work. It has to see a lower voltage reading from the rear sensor in order to determine that the cat is working properly. Removing or partially removing the rear sensor from the exhaust stream effectively lowers (or is it raises... I can't ever remember which way that goes ) the voltage that the sensor sends back to the ECU, which tricks it into thinking the cat is working well, even if it's not there.

 

I can't say exactly why the code hasn't come back, but it very well could have something to do with the blockage of the front sensor.

 

see first i did buy a new front cat and i noticed that were the o2 does go they pretty much have a shield around it.. its just a piece of oversized pipe.

Now that's interesting. They must have had the same idea you had. Or is there where you got your inspiration?

Either way. It seems to have worked for you, consequences yet to be seen, hopefully it lasts.

[WoodsWagon]

You won't see better flow through a gutted cat vs a complete non-clogged cat. You may actually see worse because the exhaust velocity stalls in the open chamber of the gutted cat. I always put a piece of pipe through the middle of the empty cat body to keep the velocity constant.

 

Even if the car is throwing a p0420 code, it rarely means the cat is clogged. What it does mean is the efficiency of the catalyst materials has dropped below threshold, or it thinks it has due to the computers comparison of the front and rear o2 sensors.

 

Withdrawing the rear o2 sensor from the exhaust stream doesn't change the voltages it creates, but it stabilizes it's readings. It's still in the exhaust atmosphere, but it's sampling rate is dropped way down. That creates the illusion that the catalyst is working in the computers mind. It's looking for steady fluctuations in the front o2 sensor and adjusting the fueling to compensate but wants a smooth signal from the rear sensor around 0.5v.

[brus brother]

The dreaded P0420 hit last week on my 2005 OB with 103k miles. Cleared code and came back at 100 miles.

My 2005 OB has two front and two rear O2 sensors.

Do I need to add the spacer on both rear O2 sensors for this to work as described?

[hankosolder2]

SPECULATION CORNER:

 

I'm guessing your OB is an H6 engine? Dual catalysts? Does the code specify which bank? If so, I guess you could just space the rear 02 sensor on the side that's throwing the code, but the other side is probably not far behind. Are the front 02 sensors fresh & OEM ?

 

Nathan

[brus brother]

SPECULATION CORNER:

 

I'm guessing your OB is an H6 engine? Dual catalysts? Does the code specify which bank? If so, I guess you could just space the rear 02 sensor on the side that's throwing the code, but the other side is probably not far behind. Are the front 02 sensors fresh & OEM ?

 

Nathan

Always like hearing from the cheap seats in Speculation Corner.

2005 OB 4 cylinder but YES dual friggin' cats.

2 front sensors. 2 rear sensors.

All original equipment at 105K miles.

Can't find the printout from Autozone (I need a leaf blower to organize my desk) but I think the readout stated 3 possiblities.

Improper AF ratio

Something about Bank 1

Catalytic converter (read: prepare to empty wallet)

[brus brother]

YIKES! Parts alone for the two cats for 05 OB/auto is close to... $1800 from discount online subie store:eek:

Is there an alternative beside cheating the sensors as above described?

[idosubaru]

make sure you don't have any leaks first.

 

Do I need to add the spacer on both rear O2 sensors for this to work as described?

i would do them both now. wouldn't be worth my time to only do one. this issue is such an annoyance i would consider it value added to do both.

 

if you were bent on only replacing one you could install it on one side....if that doesn't clear the code, then swap it or install one on the other side.

 

the fronts have bank 1 and bank 2 codes right - left and right, the rear doesn't have that distinction huh?

 

i didn't realize newer ones had two rear sensors, interesting.

[GeneralDisorder]

Are you sure your problem isnt just some leaky pipe or gaskets? Loss of exhaust before the cats will cause them to not get hot enough to work..... cold outside temps right now..... sounds plausible.

 

GD

[brus brother]

Are you sure your problem isnt just some leaky pipe or gaskets? Loss of exhaust before the cats will cause them to not get hot enough to work..... cold outside temps right now..... sounds plausible.

 

GD

@GD,

I'm not sure. It wasn't real cold when it reappeared (high 20s F) highway driving. Had gone about 100 miles and many restarts since Autozone cleared the P0420 code 5 days ago when the CEL/blinking cruise control reappeared.

Car seems to be running fine...

It is too cold to work on outside now and without a lift, I'm inclined to wait.

1. I suppose there is room above the original O2 sensor for this "extension"?

2. Is the wrench needed the standard size offered for loan by Autozone?

3. Anyone done this on 05 OB and is there a quick connect for the wire or is it cut and splice?

4. I can't recall but will the code a. reset itself b. reset by disconnecting battery c. disconnect battery and something else I can't recall?

5. Will someone come to my house and do this while I stay warm in front of the TV?

Edited December 24, 2010 by brus brother

[brus brother]

I went to Autozone and they only had 14 and 18mm. Most of the web write ups (non-subie) speak of 18mm. Is this fix for Subaru 21mm as described earlier?

Anyone able to post a part number and supplier for specs? There is discussion of using one or having to piggyback two??

AND lucky me, looks like this car has 5 sensors in all. 2 on each down pipe (PN 22641), 2 behind each cat (PN 22690)and 1 behind the muffler?/cat? right after the two pipes join, also PN 22690.

So now do I do all 3 rear sensors?

Could they have made it any more complicated?

Edited December 25, 2010 by brus brother

[Buick350X]

Geese so many post and not one jokster???

 

Code 420

 

Its your Subaru telling you to pull over and smoke another one

 

-------

 

Our bank 3 I think last cat in the line O2 went bad, problem was the threads pulled out of the cat, which meant a new cat or rigged, got it in, would not tighten, put a tack with a welder to ground it and keep it in place, JB weld around to seal it. worked ok. But needs changed again

 

Used a cheap knock off $20 uni one and it didn't last long.

[GeneralDisorder]

18mm non fouler.

 

Yeah - just do all three.

 

And yes you are making this way too complicated.

 

1. Drill through the non-fouler with a 1/2" bit.

 

2. Unscrew sensor(s) using an open-end wrench, Ford wrench, crescent, etc

 

3. Thread sensor into non-fouler.

 

4. Thread the assembly back into the exhaust and tighten.

 

Done. Takes about 15 minutes.

 

GD

[brus brother]

18mm non fouler.

 

Yeah - just do all three.

 

And yes you are making this way too complicated.

 

1. Drill through the non-fouler with a 1/2" bit.

 

2. Unscrew sensor(s) using an open-end wrench, Ford wrench, crescent, etc

 

3. Thread sensor into non-fouler.

 

4. Thread the assembly back into the exhaust and tighten.

 

Done. Takes about 15 minutes.

 

GD

15 minutes? Great, I'll be right over... take me about 5 days from Connecticut.

Thanks for the clarification on the size.

[brus brother]

Well that was easier than I thought. Part# 42009 from Autozone's Help aisle. We just had 13" of snow (a dusting to members from Alaska) but I found a clear spot in the driveway and could access the O2 sensor by removing the wheel. Wanted to give it its best shot so I used the 2 anti-foulers in the package, drilling out the one as described and piggybacking it onto the first and used anti-sieze as instructed.

The code P0420 in the Autozone readout specified bank1 so I took a chance on the mod for just the sensor behind the passenger cat since AZ only had one package in stock. If the code returns, I will do the driver's side as well as the rear sensor behind where the dual exhausts join, hopefully on a warmer day.

Thanks for the help.

[WoodsWagon]

You don't need to piggy back them, I've seen an 02wrx with no cat running just one on the rear sensor. You could pull the piggy backed one, drill it, and throw it on the other bank.

[brus brother]

OK 600 miles codeless after P0420 mechanical fix (anti-fouler) and today I got two P2096 codes (second one reads P2096P) and some at nasioc report this being related to 05 (with O2 cheaters in place). http://forums.nasioc.com/forums/showthread.php?t=1131438

I will take the advice to remove the piggyback, drill it and use on driver's side cat and probably get another one and use on the third rear sensor behind where the dual exhaust joins.

Has anyone dealt with the 05 before? I will post back or edit but I read somewhere that it has something to do with how the 05 reads the difference between the sensors that varies from other years. Just my luck...

Any thoughts?

Edited January 12, 2011 by brus brother

[RAYJAY]

on the 18mm non fouler any know where to get stainless steel one's ???

 

the brine they paste our roads here has taken a toll on mine .....and when they rust off they suck to remove ...don't even ask me how i know ....Jeff