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Old 11-11-2009, 01:18 PM   #136 (permalink)
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Default p0420 today

06 forester 2.5x. Is the front A/F(O2) sensor in the exhaust below the power steering pump in front of the engine(centerish of engine pointing up)? If that is the case is the rear O2 on the passenger side about 12 inches down and around a 90 degree turn from the front O2 sensor below the #1 plug?

Found exhaust diagram on scobymods. This appears to be the correct sensor placement. I didn't expect the rear sensor where it is, that far north in the exhaust. Not used to double cat either. 57k miles, first problem with car, have not looked at it much other than scheduled pm.

If my assumptions are wrong, correct me. The dealer wants $100 to diagnose the p0420 code. Sensor related fix on me, actual cat is bad it is still warrantied. I do not have an obdII reader. If I purchase one for this use and future uses(one that shows live data on pc), is there information where i can tell if the data is within specs?

Last edited by oncechevyguy; 11-12-2009 at 11:43 AM. Reason: found more info
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Old 11-11-2009, 07:03 PM   #137 (permalink)
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I have a 2002 Forester L standard with about 130,000. The code came up on mine also for the Po420. Actually what I need to know if I have a mechanic fix the issue if eventually it becomes the cat what would I expect to pay? I already know the Subaru dealership price and it seems a bit expensive. Also if I have had my timing belt replaced and Subaru did the headgaskets what else might have to be replaced for the milage? My Subaru has been well taken care of and I would like to keep it. I just am not looking forward to being out lots of money every month.
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Old 11-12-2009, 03:54 PM   #138 (permalink)
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Why not just do the mechanical fix? $5 and an hour of your time and problem solved. A cat is going to cost you big no matter where you get it, and may not solve the problem permanently if you read this entire thread. I'm usually not one for band-aid repairs, but in this case I did it, it worked, and I'm in love with the idea.
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Old 11-18-2009, 07:12 PM   #139 (permalink)
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Another P0420 problem on a 2005 Forester X about 88,000 miles. This one started after leaving the car outside and had some P0302, ..., P0304 errors. The car would run rough for a bit, eventually the CE light would go out and the car would run fine. After the third time the car again ran fine after a bit but now the CE light stayed on. Codes were 0420, 0302, 0304. I replaced the plugs, wires, and coil. The car runs much better, and no problems leaving it outside. Still had all the codes after a month of daily driving. Used a code reader at autozone to erase all the codes. Immediately after starting the car, it would not idle, and stall when pushing in the clutch for stops.... The CE light stayed off for a few days, with the stalls . Then the CE light came on, only code was a p0420 (Pending???) and the idle is much better, no longer stalls. Any ideas on what to try next? PCV valve has never been replaced. Otherwise car runs well. Thanks in advance.
Thought I'd follow up with the outcome... After replacing front o2 sensor, PCV value with out any success I gave up and went to the local dealer. They ended up replacing C Converter, rear o2 sensor... all under the recent recall. http://www.subaruforester.org/vbulle...ies/woohoo.gif
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Old 11-25-2009, 04:52 AM   #140 (permalink)
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From my Jan 09 post:


A long term follow-up. I installed the $5 fix and cleared P0420 in early 09. Car was temporarily assigned to my son and daughter in college mid year when they had some car problems. They advised the Forester had developed a loud exhaust noise. When I got the car back after 4-5 months recently, oil had not been changed, exhaust sounds like a dragster, and steering gear boot was ruptured.

I determined that fixing the steering gear boot would be easier if I removed the Y-pipe and catalytic converters. When I dropped the assy, the connection between the Y-pipe and forward converter was completely loose,...one nut was missing on a bolt. Boot repair was uneventful and boot had apparently only ruptured recently since steering rack and gear housing was clean. Subaru OEM boot and screw clamp worked well. I purchased new gaskets, and replacement nut for exhaust flange connection and reassembled Y-pipe and converters and re-installed.

It occurred to me that perhaps the reason for reappearance of P0420 in Jan09 was the joint leak (ahead of converters!). I decided to remove the $5 fix and see if P0420 returns. So far no P0420, however I've learned that this code may take weeks to a month to present, so I'm not ready to declare the joint leak was the reason for my P0420 in Jan, but it's definitely a possibility.

regards
Another long term follow-up. Code P0420 has not returned after over a month of regular driving w/o the $5 fix. Looks like the exhaust leak was reason for the P0420 w/ a relatively new Eastern Catalytic converter.

I agree w/ Ferret on the quality of the Eastern Converters. The support bracket on the converter pipe failed in fatigue, and I had to rig a large, 4.5" OD hose clamp to support the converter to the body support point.

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Old 12-02-2009, 05:04 PM   #141 (permalink)
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Ummm, O2 sensors are supposed to be replaced at around 100,000 miles. When they get old, they get "lazy" and don't work as good and start lighting the dash light. This also negatively affects your gas mileage. It's a wearing part, so if there are no leaks or nothing else obvious, do that first since you need new ones anyway. They aren't that expensive if you mail order them. Amazon sells tham cheap enough. I've always used Bosch replacement ones and they have worked great for me.
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Old 12-17-2009, 11:52 AM   #142 (permalink)
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Okay...so I've had the catalytic converter replaced, as wellas both the front and rear O2 sensors.

The car seems to run okay...except every once in awhile, the damn CEL comes back on with the P0420 code. I can erase the code, but it comes back...maybe within a week....or maybe not for a couple of months...but it keeps coming back.

Any idea why? The local mechanic I use said that after a searching around, he had heard that there might be a onboard computer update for this, but that it would have to be obviously done at a dealership.
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Old 12-17-2009, 04:26 PM   #143 (permalink)
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Pre-cat exhaust leak?
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Old 12-17-2009, 06:42 PM   #144 (permalink)
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I suppose it could be a leak. But wouldn't that show up more often then?
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Old 12-18-2009, 03:12 AM   #145 (permalink)
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All that money wasted...do the mechanical fix and end your worries. :)
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Old 12-18-2009, 05:21 AM   #146 (permalink)
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I suppose it could be a leak. But wouldn't that show up more often then?
^ Unknown - it may take a bit of driving (however the ECU determines drive cycles for this particular CEL/DTC) before the light starts flashing.

That's how it was with my previous "Stage II" setup, where the tuner did not disable this CEL. If I ran her without the mechanical fix, she'd eventually pop the code, but it wasn't anything that was predictable by my count (I'm sure that if I were the ECU, I'd have been able to predict it ).
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Old 12-18-2009, 07:50 AM   #147 (permalink)
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The local mechanic I use said that after a searching around, he had heard that there might be a onboard computer update for this, but that it would have to be obviously done at a dealership.
Well, this is what I heard about the ECM flash. But there is no definitive answer which I could find. So I did the mechanical fix, only had the code once in 12 month period and it was probably due to some other strangeness.
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Old 12-18-2009, 06:45 PM   #148 (permalink)
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Originally Posted by ruzicka View Post
Okay...so I've had the catalytic converter replaced, as wellas both the front and rear O2 sensors.

The car seems to run okay...except every once in awhile, the damn CEL comes back on with the P0420 code. I can erase the code, but it comes back...maybe within a week....or maybe not for a couple of months...but it keeps coming back.

Any idea why? The local mechanic I use said that after a searching around, he had heard that there might be a onboard computer update for this, but that it would have to be obviously done at a dealership.
Same situation...at the beginning of November I had my cats replaced (got mine from that place in Canada on eBay that I believe Ferret pointed out) as I knew I probably wiped them out when a plug went bad earlier this year. I was dumping fuel in it when the CEL was flashing until I could replace the plug, as I was on a long trip. Sucky...but anyway...replaced both sensors as well. Just a few nights ago, I was cruising home from work and using the go pedal gently at around 55 mph and my dash got a little brighter on my '01 L. Man was I pissed!

So it appears this is a saga with these mean machines. Not fond of the "rigging" method to get around this, so I may have the garage check for any possible leaks, and hoping the rear sensor isn't junk that I bought. Extremely tight right now as I need some other work yet including new accessory belts, front left axle, struts all the way around, inevitably new tires, steering rack is worn, blah...but I must say she's been good as the 2nd owner with 122K of my own miles out of the 179K she has on her.
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Old 12-18-2009, 06:53 PM   #149 (permalink)
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^ The thing that made me pursue a re-tune, in terms of this specific concern, was that in using the mechanical "fix" for the rear-O2 CEL, my fuel trims were off. Although, theoretically, this should not mean anything more than slightly worse fuel economy, I couldn't help but think that I should have it addressed :reface", which is why I did it.
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Old 12-19-2009, 07:22 AM   #150 (permalink)
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^ The thing that made me pursue a re-tune, in terms of this specific concern, was that in using the mechanical "fix" for the rear-O2 CEL, my fuel trims were off. Although, theoretically, this should not mean anything more than slightly worse fuel economy, I couldn't help but think that I should have it addressed :reface", which is why I did it.
By "re-tune", you mean just an ordinary tune-up? So far, I still haven't found any reason for the CEL to still be coming on with the P0420 error code. They've looked for leaks as well several times. I'm not really into the "$5 fix", as I prefer my Forester to operate the way it was designed to. Maybe I should take it in to the dealer to see about any onboard computer updates.
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