P0420 - Catalyst System; Bank 1: Efficiency Below Threshold

[sil8ty]

pictures of spark plug added, look back on top of page 2.

I've included some pics of what your plugs should look like, if everything is OK

Edited February 19, 2012 by sil8ty
including pics

[ripitAWDday]

sill8ty , try running some cleaners through your engine. when you put the cleaners in your tank be sure to drive for a good while maybe an eighth of a tank to ensure the cleaner gets a good run through the warm system. that can clean up your spark plugs and get general gunkiness out of your engine and improve burning efficiency. other wise my mate, with that many miles beware a head gasket leak. best way to check for that is overheating and mixed fluids. coolant in oil/ oil in coolant.

[octain11]

ya that would be a good idea, run a seafoam flush in your car, 1/3 can through the master cylinder pvc, 1/3 to transmission, 1/3 inn gas tank, make sure you got someone to help you control the engines rpm and be careful you can hydrolock the engine so poor it in very very gradually

[sil8ty]

You guys missed it, the one I pulled out is at the top of this page,and also in this comment. It is what's considered too hot. It's not the engine, it's fine, no coolant problems.

 

The spark plugs are running too hot (not the car) and can be noticed since it's totally too white. The above 3 spark plug pictures are proper spark plugs (copper though) of what you should get

if you have proper timing/gaping.

Iridium type plugs are what Subaru uses are harder to deform, but the one ones I pulled out were deformed

because the gap has shortened.

I believe that's the cause of my po0420 fault.

Edited February 22, 2012 by sil8ty

[ehsnils]

Overheated plugs is the symptom - and that is usually caused by a too lean mixture.

 

Too lean mixture can be caused by air leak (like too much air leak after MAF), one single injector running too rich causing the O2 sensor to lean out, one single injector running too lean (only one plug will get overheated) or bad O2 sensor.

 

There are of course other causes too but the ones I listed are the most common.

[sil8ty]

I thinking this may be something alot of Subarus may be experiencing and how many people do change the spark plugs since the expected lifetime of the plugs are very long. Iridium plugs may last longer as a metal, but it's not as good as an electrical conductor.

I'm thinking it may have happened overtime, it's been close to 140000km. I'm running all stock on this car except GT brakes.

[protivakid]

I am chasing this down in an 01 legacy w/ the 2.5. As part of general maintenance and trying to solve this I have changed the following since the code started:

 

-Alternator

-Battery

-Upstream O2

-Downstream O2

-Spark Plugs

-PCV

-Fuel Filter

-Air filter

-Radiator Coolant

-Regular Full Synth Oil Changes

-Ran Seafoam through Oil & Gas

-Timing belt job w/ water pump

-Headgasket job

 

Problem started a year ago before doing any of the above and if I clear the code it will come back in 1000 - 3000 miles.

 

Watched this video where a guy talks about this code on a 3.0

 

I tried logging some O2 data but the numbers seem to be different than the values in the video.

 

I am not sure what's left to check and suspect I may actually just have a bad cat. I guess I could pull the new plugs I threw in during the fall and see if there are signs of running too lean.

Edited January 26, 2015 by protivakid

[johnegg]

-Upstream O2

-Downstream O2

 

what brand of o2 sensor did you install?

the front one needs to subaru quality or much better.

the rear can be generic.

 

if a quality sensor was used,

then it might be time to install an anti fouler spacer.

it is a work around and not a fix.

but it should eliminate the CEL.

 

read this:

P0420 Diag - Subaru Outback - Subaru Outback Forums

[protivakid]

The front sensor was a BOCH that was on there for YEARS without a problem. I put in a new BOCH and still have the same problem. Given the old sensor ran so well for so long without any CEL and after the new one the car is doing the same it sounds like I have an issue someplace else.

 

I have heard a few mention using a defouler but I would really like to fix the issue if at all possible and not just mask it.

 

The price of a cat is steep but if that's really my issue I can eat it. I just dont want to throw in a new cat to have the same code pop up.

[johnegg]

The front sensor was a BOCH that was on there for YEARS without a problem.

how long did you drive the car with no p0420 cel?

did the bosh sensor come with a plug on it?

 

The price of a cat is steep

 

it is highly unlikely that it is the cat.

 

look for an intake leak.

spray carb cleaner around all the air intake parts,

air filter,

plastic piping

intake manifold gasket

throttle body gasket

Edited January 27, 2015 by johnegg

[protivakid]

how long did you drive the car with no p0420 cel?

did the bosh sensor come with a plug on it?

 

 

 

it is highly unlikely that it is the cat.

 

look for an intake leak.

spray carb cleaner around all the air intake parts,

air filter,

plastic piping

intake manifold gasket

throttle body gasket

 

I got the car in 2010 w/ 120K on it. The code started in Feb 2014 when I had ~ 185K on it. With this I know the sensor that came with it was at least good for 60+ thousand miles. And it would also seem strange for the new sensor to be bad right out of the box producing the same symptoms as the old. The new sensor was direct fit plug wise just like the one I removed.

 

For an intake leak my 01 legacy only has a MAP no MAF so unless I am mistaken my only point of leaks would be from the air filter assembly onwards where vacuum / small air hoses start to connect. Everything prior the filter is plastic ducting only.

 

Taking off the manifold seems like a pita. Any easier way to check the gasket? I'll try to check out the TB one as well.

 

If by odd chance it was a bad cat, is there a good way to tell? I live in the salt belt so things get pretty bad under there but I don't hear any loud exhaust leaks.

[johnegg]

these cats rarely go bad.

most shops / the dealer will tell you that a p0420 means you need new cats,

but usually a new rear o2 sensor will eliminate the code.

there are lots of things that will cause this code besides cats.

 

did you read / view the linked posts?

it is a lot, but worth it.

you probably do not need all of it,

the original poster is very knowledgeable,

if he says it is so, then it is.

 

 

spray carb cleaner all around the intake and vac hoses when idling to find a leak.

if the idle revs up you have found your leak.

Edited January 27, 2015 by johnegg

[johnegg]

I have seen a number of vehicles come in with the 420 code and it ended up being the gasoline. A lot this time of year when the oil companies are switching to winter blends.

 

Mostly through the year it is, in decending order of repairs,

thermostat,

plugs (or other ignition),

filters,

exhaust or intake leaks,

injector seals,

injector(s),

MAF/MAP sensors,

rear O2,

AF sensors on Japanese cars,

front O2 on others,

and lastly the CAT.

.

posted by cardoc, subaruoutback.org , nov. 2012

[protivakid]

.

Mostly through the year it is, in decending order of repairs,

thermostat,

plugs (or other ignition),

filters,

exhaust or intake leaks,

injector seals,

injector(s),

MAF/MAP sensors,

rear O2,

AF sensors on Japanese cars,

front O2 on others,

and lastly the CAT.

posted by cardoc, subaruoutback.org , nov. 2012

 

Thermostat seems to be working properly. Temp is fine and coolant seems to be flowing great when it opens up.

 

Filter has been replaced.

 

Will crawl under and check for exhaust leaks but not hopefull.

 

Will a bad injector show signs of running lean on the plug? I've seen people do a test by holding a screwdriver to it and listening for when it fires.

 

Any way to check a MAP?

[protivakid]

Thermostat seems to be working properly. Temp is fine and coolant seems to be flowing great when it opens up.

 

Filter has been replaced.

 

Will crawl under and check for exhaust leaks but not hopefull.

 

Will a bad injector show signs of running lean on the plug? I've seen people do a test by holding a screwdriver to it and listening for when it fires.

 

Any way to check a MAP?

 

Looks like this will help me check a map -

 

For injector o-rings I read you spray a little carb cleaner around where the injector meets the head while the engine is running. If the idle changes you know there is a leak. This accurate?

 

This test also looks like it will tell me if the injector is firing

 

Last I ordered a cheap OBD2 to USB cable so hopefully with my laptop and some software I can grab some good live data. My cheap handheld scanner only gives a few things.

[diverrick]

Just so you guys all know running the car with a bad head gasket, (like I did) causes anti freeze to be burnt, and thus ruins the cats. I am having this same CEL issue right now. 2004 model Changed the wires and plugs, seeing as they had 225,000 miles on the originals. Cleared the code. It came back after about 15 days of driving. LOL got my money out of those plugs. Today I'll change out the Rear sensor and clear the code again. We'll see if it comes back. In that case, I'll have to buy the cats I guess. Damned expensive from Subaru. And they will not ship me the perfectly good ones online, to commifornia. My plan is to have them shipped to my buddys place in Oregon, then he'll ship them down to me. They meet all the standards for California so I don't get why I cannot buy them here. Maybe someone can explain that to me.

[Matty2Hotty]

Well I'm joining the club... But another question to the Cat code... Someone replaced the cats and there is no rear O2 sensor as my other 3rd gens after the 2nd cat where the circle cutout is in the heat shield point towards the driver side. No wires, nothing over there but there is a threaded plug in the cat pipe.

 

Found the rear O2 right after the 1st cat behind the first O2 sensor. This just doesn't seem right, how many people have their O2 sensor right after the 1st sensor on the same main cat? I don't have any wires and the O2 wires are no where close to reaching the rear cat location for me to swap the plug and install the rear O2 back on the 2nd cat location. Ideas?

[RustyRuu]

bump- did you ever figure this out matty?

[Regardie]

California Spec Subarus have the rear O2 sensor after the first cat, federal spec put it after the second cat. Check your label on the hood to see if you have a 49 state or California spec emissions system.

[RustyRuu]

thanks regardie,

 

nice little fun fact there...

 

i was more asking if he bought new sensors or cats or just put a spacer in...

 

I am now in the P0420 club, as well as new to the 200k miles club (for subaru's at least)

I Had this code some 8k to 9k miles ago. tore my motor apart rebuilt it and it just now came back noticed it after getting into the 4k rpm range which i dont do a lot...

 

my idea was to get a anti fowler/spacer to figure out if its the cats or the sensor. if its the sensor, as in i'm still getting the code, it will be replaced. if its the cats, the code goes away, i will spend my time instead of money and they will be hallowed out.

 

Good idea so far? anyone else have other ideas?

[RumbleRumble]

You can always take the cat pipe off (one side) and shine a light to see if it's cracked/clogged.

[albertothe16]

MY 2005 SUBARU LEGACY i HAD FEW CODES P0420, P0137 AND P2096 ON BANK 1. I REPLACED THE O2 SENSOR AND REPLACED THE CATALYTIC CONVERTER. BUT THE P0420 CODE STILL THERE BUT DOES NOT SAY ON WHICH CAT. I WOULD LIKE HELP ON HOW FIND OUT WHICH ONE COULD BE?

[GunFunZS]

I have the cali H4, and get this code intermittently

 

Sounds like I need a downstream O2 sensor and it needs to be the cali model. Aprox $25 dollars and brand isn't critical. If that doesn't fix it, then go to the next thing.

 

Also, need to buy a code reader so I can clear this stupid code and not have to pull a battery terminal on trips. Someone needs to punish the engineer who decided that CEL= no cruise control for you. What a jerk.

 

Unclear whether cat is original or what. I'm not the first owner, and stuff may have been replaced. Any easy visual way to know whether I have OEM cat while I am swappign out the 02 sensor?

 

Is that right, or am I making some 'tarded oversight?