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I have a 2003 Outback 2.5 cylinder that has 231,000 miles on it and it began vibrating when accelerating last week while on a road trip. It isn't all the time during acceleration, at a particular speed, or RPM. I can tell it is when I am trying to push up a hill or just a little more gas. I don't think it is plugs. It isn't bad yet but I needed a new axle as well so I took it to the dealer so they could diagnose the problems for me. They agreed that I needed a new axle and that I needed to get my catalytic converter replaced. I did have a couple of error codes that indicate a problem and I have seen several posts about the P0420 code. Some say that it is the O2 sensor and others say the cat. I replaced the O2 sensors about a year ago so I don't know if that would be the problem. Before taking it from the dealership, I asked them to reset the codes for me. I have been driving it around all day and the CE light hasn't come back on. Anyway, I don't want to drop $1000 on a new cat for this old car and was wondering what the consequences would be for taking it to a muffler shop and have them remove the cat and running a straight pipe. What do you think? Will this impact the gas mileage, performance, sound, etc.? Do you have any other suggestions?
 

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Vibrating when accelerating is the inner joint of the axle. If the boot is broken (usually is) then that verifies which side.

1. you can reboot it and the vibration will go away, done it a bunch of times. it's only vibrating because it's out of grease and heating up - not because it's failed....regrease it and you're golden - i am speaking from lots of experience.

2. do not use an aftermarket axle, they're terrible. if you don't believe me, google or search any subaru forum to verify. the original Subaru axles are very robust and should be retained. the rebooted vibrating axle (vibration would go away once some fresh grease is in there), would be higher quality than a high percentage of new aftermarket junk. problems out of the box are common.

3. if you need another axle - buy a used Subaru axle with two intact boots and replace the boots with new boots. i get original Subaru axles all the time for $25 - $33 each and install new boots. Car-Part.com--Used Auto Parts Market

4. i'll take your old axle if you wanna sell it.

5. dealer axles are really expensive. the only non-dealer alternative that is good - is MWE out of Denver, Colorado. about $70-$90 plus shipping and core for axles. annoying but worth it to avoid the aftermarket debacle.

P0420 code is a joke (in all manufacturers this is an issue, not just Subaru - you can google and read about it all day long):

1. ignore it. zero damage possible. 1980's Subaru's have zero issues even though they don't even have a rear O2 sensor to generate this debacle of a code. the sensor causing this code (rear O2) is not even USED by the ECU, so it's not that it "doesn't" cause issue - it can not cause issues with performance or gas mileage. ***(see note below). drive 100,000 miles with that code on, doesn't matter - it's done all the time and is benign. complete waste of $1,000 to pay Subaru to fix it.

2. install the $5 fix and be done with it. search here or google - very common.

3. if you have any exhaust leaks - fix those and that will likely cure it.

4. installing straight pipe is fine, you just may have the code forever, so you must live in a state that doesn't look for the check engine light.

5. the code will come back, they generally start being randomly intermittent like this, very common. might be 1 week, 1 month, 1 year, 3 years but it *WILL* come back.

6. Subaru has a very detailed smoke-involved machine/process for properly diagnosing this issue...i would never do it in a million years, but be sure you don't take their recommendations without that specific test and results done properly. They may just "guess" or hope it pushes you to buy new.

The tolerances required for this paramter are way too tight and aren't practical for real world usage. What rolls your eyes is that cars like yours which have this catalyst inefficiency code would actually pass an emissions test if you did the gas analyzer, sniffer test. but of course they won't do it with the light on....so, people are spending thousands all over the country to fix this code which isn't actually even violating emissions requirements. It's not polluting - so let's pollute the environment with increased factory, recycling, gas, chemical, and land fill usage. way to be green, high five!!

That's why the $5 fix is so acceptable for anyone that understands this issue.

***(The situation where a severe engine problem is causing some other issues which trigger the P0420 code does exist - but they are almost entirely theoretical and not practical or seen in real world usage. and you would likely have made some comment about your engine being a piece of junk for some reasons)
 

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On the O2 sensor light if you remove the cat.....I have a Honda S2000 and put a "test pipe" in place of the cat. I was told to screw a spark plug anti-fouler into the pipe, then screw the 02 sensor into that. I never had my light come on after I did this. :)
 

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On the O2 sensor light if you remove the cat.....I have a Honda S2000 and put a "test pipe" in place of the cat. I was told to screw a spark plug anti-fouler into the pipe, then screw the 02 sensor into that. I never had my light come on after I did this. :)
that was what i was referring to here:
2. install the $5 fix and be done with it. search here or google - very common.
tons of information all over the internet and the parts are available ready to install on ebay if you don't want to make/drill your ow.
 

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read the P0420 thread a few down. The code comes from something else not working. You need to correct that. Unlikely it's the actual catalytic converter. Just spacing off the rear O2 fixes the symptom but not the cause. You really should find out the cause.
 

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P0420 wouldn't be an issue if you don't have emission testing.

It won't be an issue until the CAT clogs with carbon and your engine can't breathe.

It won't be an issue until you start seeing you fuel economy drop because your engine isn't maintaining proper temperature and the ECM is dumping fuel into it to try and warm it up.

It won't be an issue until something else happens with the car either engine or transmission and you won't know it because the light is on all the time.

It won't be an issue until the engine is so far gone from poor maintenance that you've replaced it with a new car.

Find and repair the problem. There is no $5 fix. There is a $5 cover up and ignore it. And you shouldn't ignore your car. You depend on it too much.

Read this thread, then we can get back to finding the problem: http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diag.html .

And I don't work for a dealership. I actually help people find the real issues for a living, not cover it and take your paycheck.
 

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bang the cats with a hammer then blow the carbon out on the highway...it might help your cats last a little longer, but they need to go or be replaced.
 

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bang the cats with a hammer then blow the carbon out on the highway...it might help your cats last a little longer, but they need to go or be replaced.
I wouldn't bang the cats with a hammer. They are pretty delicate components that are adhered to the shell. Break that adhesion, and you will subject the inner 'honeycomb' to vibration. Eventually, you will have an empty cat shell.

The P0420 code can generate form a bad tank of gas, so it's generally not to worry about. Just clear it and move on.

In a nutshell, the code is generated when the ECM sees abnormal readings from the O2 sensor situated downstream of the cat. The upstream O2 sensor is the busy one that sees instantaneous exhaust samples and feeds this information to the ECM. You will notice much more active crossover counts on the upstream sensor. The ECM takes this info and adjusts the injector pulse width (among other things) accordingly in an effort to maintain proper air/fuel ratio. The downstream sensor is essentially the ECM's way of checking to make sure it is doing its job correctly. The ECM also works on historical data. Some terms for this may be "Block Learn" or more commonly "long term fuel trim". It uses this historical data to adjust the engine's performance as it slowly wears over time. That's why it takes typically 3 full drive cycles after resetting the ECM for it to find its way back to its happy zone.
 

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Who is cares if it's grave digging. My sub is 14 years young and the cats just started to plug up. The back pressure broke the welds and gaskets. Oddly enough, a bad downstream O2 sensor will actually give you better might because the ECMs answer is to lean the fuel/air mix because it thinks there is too much unburned fuel downstream.

I hear talk about reaming out the cats, but what are you using to do that? A drill? Isn't there a honeycomb of platinum in there?
 

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Also, I didn?t really mean bang. I ment tap them with a hammer front to back, top and bottom, just to dislodge some of the large carbon chunks. Then blow out the carbon. You may have to tap the back cat again because some of the carbon dislodged from the front cat gets caught in the back cat. I did this and after 3 or 4 trips the idiot light went off. The exhaust sound noticeably changed too. You can also remove and clean the rear 02 sensor too and take a test trip with it removed.
 

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Who is cares if it's grave digging.
right, no one cares. thought i'd save folks from thinking the OP needed help, which replies suggest a current topic/question. a tip may get better presence, search results, and be more useful in a thread of it's own.

I hear talk about reaming out the cats, but what are you using to do that? A drill? Isn't there a honeycomb of platinum in there?
rebar type materials.
 

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Go to NAPA, pick though their remans and purchase one of the OEM "Green cup" axles for $50 or so. It'll last a LONG time(I've used 3 or 4). As for the 420(ironic) code? No $5 fix here...too rich for my blood...how about a $.001 cent fix? A tiny piece of electrical tape to cover the annoying orange CEL. I've had one on the '00 for about 100k. I randomly check for codes just to make sure...but if it's running fine(which it usually is)...I don't worry about it.
 
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