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2010 Forester
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12 Posts
My recent experience with the 420 code = 2010 Forester, did the $5 fix, still threw code. Only used 1 plug fouler, perfect!!! Even starts better
 

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2006 Forester
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131 Posts
Still trying to avoid putting in a new cat system with sensors. Does anyone KNOW what the normal ECU values should look like? (I ran a report from a scanner, and have a 45 mile dataset)
 

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2005 Forester X and XT Manual and Auto
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1,046 Posts
Just some experience on this - i did this years ago on my daughter's 03X and it worked. You have to be careful about the non-fouler you use, or protecting it, as mine rusted out VERY quickly and ended up breaking off, bottom half still threaded in the bung, rusted to hell so could not get it out on my own. - of course CEL returned since o2 sensor was dangling lol. I then went to the homemade resistor fix, which actually worked for awhile (it cleared the code on its own) but later the CEL returned.

Anyway, currently the car is about have a family friend's shop fix the exhaust leak from the bung at least, of course i'll have some explaining to do....those headers have been fun, but been a pain dealing with this.
 

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Administrator
2007 Forester Sports XT 4EAT
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2005 Forester X and XT Manual and Auto
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@2.5x_sleeper Wow that area of the car has never dreamed of looking that good since it left the dealer lot i would imagine! I'm in SE VA - not the rust belt but we are humid and do get occasional snow, also pretty much surrounded by salt water. If i did it over again, i would at least try some high temp paint on it. I'd wager a big part of it is your meticulous vs my not-so meticulous maintenance though :wink2:
 

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2007 Forester Sports XT 4EAT
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@NinoS those picture were on the project reinstallation, so it's going to look like new, as most of the parts were new & mostly stainless steel.

We do spray our exhaust, excluding the CAT, with Rust-Oleum B-B-Q black, which is a high temp paint. Very easy to do, as any over spray blends in with the undercoat & dirt!

Being in a "salt free" area make a huge difference!

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 
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2009 Forester 2.5 Premium Crappy 4EAT
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259 Posts
Well, my turn to add on to this wonderful post. I recall first reading of this "Fix" when I had my '05 5spd. It ran great when it was being used, but sadly, it sat a great part of it's life sitting in airport parking garages. I did encounter this wonderful code while I owned that car (from new). I'd say the code appeared around the age of 10 and about 110000 miles. Rather than do the fix, or even replace the cat, I opted to just buy a scanner so I could reset the code on the fly when commuting. A couple years ago, I swapped the '05 and bought the wife a new CRV. I got her '09 Forester 4EAT Premium. It was was good for a year, then with about 115000 miles on it, I get the code. This time I got a few others as well, from the front sensor. All things together, the cat was bad, the exhaust was rusted out. So, full replacement (went aftermarket). About 7-8 months later, I get the code. So, I swap out the old 02 and the code goes away for awhile. Then I get a horrible misfire problem. Sadly, I drove with that for awhile, and think I may have cooked the cat. Anyway, this past Saturday I did the $5 fix. Prior to this, with the scanner connected, I get the code about every 10-15 minutes of driving. Two start stop cycles yesterday and my normal 35 mile commute this am, with scanner connected, I get no codes. I know that there is the warning about using this fix on '05+ vehicles, but I am in the market for a replacement soon, and at almost 11 years old and 148000 miles, I am not too worried. This fix is just to get me past inspection, then if the car performance suffers, I might remove it. My take-away from this is not directly cat related, but I truly believe my issues come from two things. 1. cheap after market cat. 2. Ignoring drive-ability issues like misfires, etc.
 

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2005 Forester X
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57 Posts
This might be a stupid question, but I had a buddy who did a similar fix on his car (a mazda mx5 if I remeber correctly) to get rid of a code, and it made it burn really rich which eventually fouled up his spark plugs. If we do this to the downstream O2 sensor, we would have no risk of messing with air/fuel mixture as that corresponds to the front sensor right? Just trying to clean up my paranoia in the back of my brain before I try this fix...
 

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2007 Forester Sports XT 4EAT
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@Jfunk I'm assuming you know this is not a fix, but a workaround & could mask a problem that should be addressed. With that said, did you read this post in this thread?

As noted in that post I linked you to, some member with '05+ have had good luck with the $5 fix, so you could give it a try. It's easy enough to remove if you have issues.

If the engine run too rich, you should notice a reduction in your gas mileage.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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2005 Forester X
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57 Posts
@2.5x_sleeper Yes I suppose fix is not the right word. The only code my car is throwing at the moment is the PO420 and I did the upstream sensor last year to fix a running lean issue so I think (and hope) I don't have any other problems to mask. As per the quoted post, I did not see that one. Thank you for pointing it out. I think I will try it and keep my eye on my fuel economy. Like you said, it looks quite straightforward to switch. I've had the PO420 for much too long and its time to at least try something (and use cruise control again :p). I'm fairly sure that its a worn out cat that's throwing it, the car does have 230k kilometres after all. Thanks for the insight! Greatly appreciated!
 

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2007 Forester Sports XT 4EAT
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40,534 Posts
@Jfunk assuming your gas mileage is normal, as is the engine performance the $5 fix might be worth a try. The $5 fix... most likely $10 fix now, is easy to install & just as easy to remove it causes issues.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,070 Posts
This might be a stupid question, but I had a buddy who did a similar fix on his car (a mazda mx5 if I remeber correctly) to get rid of a code, and it made it burn really rich which eventually fouled up his spark plugs. If we do this to the downstream O2 sensor, we would have no risk of messing with air/fuel mixture as that corresponds to the front sensor right? Just trying to clean up my paranoia in the back of my brain before I try this fix...
If you put the spacer on the front sensor then I can see an issue as that one controls the A/F mixture, on the older models the rear sensor (after the cat) is strictly to see cat efficantly from what I understand and does not send a signal that controls ecu aspects. I've had this fix on my kids 2001 Forester with 200K plus miles for the past 2 years. No issues other than every once in a while the code will pop up again. Seems random but I'm going to say maybe every 4-6 months. I have a code reader and erase it for him.
 

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2007 Forester Sports XT 4EAT
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40,534 Posts
@Peaty on the '05+ the rear O2 sensor is also used for fuel trim. See my update on this post in this thread.

Some members have had suscess using the $5 fix on the '05+, but other members have ended up with a P2096 CEL code - Post Catalyst Fuel Trim System Too Lean Bank 1 & have had to remove the $5 fix.



Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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2005 Forester X
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57 Posts
@2.5x_sleeper Just finished installing the spacer. An acquaintance of mine (used to own a shop) actually had a leftover stainless steel spacer for this exact reason, as it is perfect length for the sensor, instead of stacking 2 plug non-foulers. Initial test drive had no surprises. We shall see!
 

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2005 Forester X
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57 Posts
@2.5x_sleeper Well, unfortunately today, the car threw the P2096 :(. I didn't notice any fuel economy or performance changes for the couple weeks I had the spacer installed, but I guess its time to take it back out and put up with the stupid P0420. I just wish that the CEL on subaru didn't disable cruise control. I suppose it's a good idea for them to rake in money from maintenance... It was worth a try!
 

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2007 Forester Sports XT 4EAT
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40,534 Posts
@Jfunk that's too bad, as some had luck with this on their '05+.

Kind of a "catch 22"... without the spacer, the rear O2 sensor is reporting too much O2 in the exhaust flow. With the spacer, it's reporting not enough O2 in the exhaust flow!

Curious... is there another CAT after your rear O2 sensor?

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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2005 Forester X
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57 Posts
@2.5x_sleeper Yes, there is another cat downstream from the rear sensor. Total of 3 on the car.
 
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