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Discussion Starter #1
Howdy Gang,

[Search Terms: o2 sensor obd p0136 $5 Fix catalytic converter]

I know this whole O2 thing has been rehashed a lot but I find I have yet another question, mostly related to my failure to follow instructions the first time around.

2001 Forester, ~130,000 miles - Two years ago my Front O2 sensor died and getting it out of the Cat stripped the threads, so it was both a new Front O2 and Cat. The back O2 I was able to re-use. Due to my failure to read and follow instructions I put the $5 fix onto the new Front O2 sensor rather than the rear.

Now, on deceleration after highway use, it pops the CEL and the OBD II code is P0136 for the rear O2 sensor. Rear sensors are expensive {reason unknown} relative to the front so I thought I'd try the $5 Fix on it first before replacing the sensor itself. As I understand it the rear is just checking to see that the Cat is still there relative to the Front and doesn't have any say or input to the brain as far as fuel mix, etc.

Question: Should I pull the $5 Fix on the front sensor while I'm in there? It hasn't caused any problems and I'm getting good mileage but now I'm wondering if the reduced gasses going to it relative to the rear are also exacerbating the whole issue.

Any advise/comments appreciated.

Alan D.
 

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Super Moderator
2007 Forester Sports XT 4EAT
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The front O2 sensor, or Air/Fuel sensor is critical for correct engine operation. You need to get the spacer off there as soon as possible! :icon_eek:

Yes, the rear O2 sensor monitors the efficiency of the CAT & isn't critical for correct engine operation. Usually adding spacers will only stop the P0420 CEL code. :wink:

Bobby...
 

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The Modfather
2016 BRZ Limited - Manual 6 Speed Manual
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Having the spacer in the front has the potential at minimum to mess up your MPG's at worst you can damage your motor. Like he said, remove it ASAP.
 

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Discussion Starter #5
Will Do, Peaty. On my list for Saturday iffin' the creek don't rise or the skys dump another foot of snow!:icon_razz:

Alan D.
 

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2002 Forester S
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Question about rear 02 sensor on 2002

First time posting, but have found this forum invaluable in the 2 years i've had my Forester.

I've been dealing with a steady CEL for a while now, with no drop in MPG or engine performance.

I was given 2 different stories by the same local dealer, first that it was an 02 sensor, and then that it was my cat.

before i change the cat, i plan to replace my front 02 sensor and do the $5 fix on the rear sensor.

Does anyone know how the $5 fix will affect a Virginia state emissions inspection?

If i have the $5 fix on the rear, and the CEL light is off, i'll pass if my cat is still good, correct? And if the cat is bad, that will show through on the VA inspection?


I'm hoping that the $5 fix won't result in an automatic fail if hooked up to a sniffer.

Thoughts/comments?

Thanks
 

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The Modfather
2016 BRZ Limited - Manual 6 Speed Manual
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jbraun,

I hate to say this but, it depends. Do they do a visual on your exhaust system? If they do and they see the fix you may fail. Also, it depends if your cat is truly bad or the sensor is bad. If the sensor is bad (chances are good) then you will pass with the caveat they don't do a visual inspections too. If the cat is bad and you have the fix you may not pass. I've heard tell of people with well tuned motors passing emissions with faulty or no cats. I would not count on it though. However, it will be a cheap way to find out if it's the sensor or the cat ;).

PS welcome
 

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2007 Forester Sports XT 4EAT
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First time posting, but have found this forum invaluable in the 2 years i've had my Forester.

I've been dealing with a steady CEL for a while now, with no drop in MPG or engine performance.

I was given 2 different stories by the same local dealer, first that it was an 02 sensor, and then that it was my cat.

before i change the cat, i plan to replace my front 02 sensor and do the $5 fix on the rear sensor.

Does anyone know how the $5 fix will affect a Virginia state emissions inspection?

If i have the $5 fix on the rear, and the CEL light is off, i'll pass if my cat is still good, correct? And if the cat is bad, that will show through on the VA inspection?


I'm hoping that the $5 fix won't result in an automatic fail if hooked up to a sniffer.

Thoughts/comments?

Thanks
I see this is your first post, so welcome to the forum from Oregon! :biggrin:

If they do a visual inspection, they may spot the spacer(s) & they may fail you. If the CAT is defective, you'll fail if they use a tailpipe sniffer, since the CAT wouldn't be functional. Still, if the CAT is marginal, it could pass. If the rear O2 sensor is faulty, you'll pass with the spacers, assuming the CAT is working properly. :wink:

Bobby...
 

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Awesome, thanks guys.

follow up question- if i'm going to space the rear 02 sensor out of the system, there is no use in replacing it, right?

here in Virginia there is a $725 waiver for emissions inspections, so if i spend more than that and am still failing inspections, they'll let me slide.

hoping the $5 fix and a new front 02 will do the trick!
 

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2007 Forester Sports XT 4EAT
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I forgot to ask what CEL code are you getting? That would help determine what the fault is & how to best address it. :wink:

There's no need to replace the front O2 sensor, if your gas mileage is normal & there's no hesitation or backfire. Some exhaust pipe sootiness is normal on the Forester, but it shouldn't be extremely sooty. :smile:

Bobby...
 

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Last time I scanned it i got the P0420 code, as well as one (i forget the number) saying the engine was running too lean.

that was right after i'd had new plugs and wires installed at the dealership.

twice i've had the CEL blink off, only to return after about 98 miles of driving (just inside the threshold where I could have gotten my emissions test)

i'll run the codes again this week.

Thanks-

Justin
 

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2007 Forester Sports XT 4EAT
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If you're getting the P0420 CEL code, that means the rear O2 sensor is detecting too much O2 in the exhaust. This could be caused by an exhaust leak (rusted pipe) ahead of the sensor or a failing CAT. Of course the CAT could be overwhelmed by the engine running too rich, but you said you had a CEL code that said you were running lean. :confused:

If you could pull the CEL code that's stored now, that would provide more info to work with. :wink:

Bobby...
 

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Bobby-

Pulled the codes last night. Got a total of three:

P0420 (bank 1)
P0130 (bank 1, sensor 1)
P0420

they popped up in that order, with the information in parenthesis as well.

I looked up the P0130, which is front 02 sensor issue...

Do the 2 P0420 indicate that both the front and rear cats are toast?


Thanks again for your help!

btw, this is a 2002 S model with 121k miles.

Justin
 

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P0420 is usually a bad rear o2 sensor, it just is saying that it's not seeing enough of a delta change between the front o2 and rear o2 sensors, if the front o2 sensor is messed up it can cause it to throw the error for the rear as well. I would replace the front o2 sensor first and then see where that gets you. Also make sure you don't have any exhaust leaks before the rear o2 sensor (possibly a leak at the headers or cat could give some errors such as the 0420)
 

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Bobby-
Pulled the codes last night. Got a total of three:
P0420 (bank 1)
P0130 (bank 1, sensor 1)
P0420
they popped up in that order, with the information in parenthesis as well.
I looked up the P0130, which is front 02 sensor issue...
Do the 2 P0420 indicate that both the front and rear cats are toast?
Thanks again for your help!
btw, this is a 2002 S model with 121k miles.
Justin
If your front O2 sensor is failing, it could be running your engine too rich, overwhelming the CAT & the rear O2 sensor will drop a P0420 CEL code.

Is your exhaust pipe overly sooty? Any hesitation or backfires? If so, that would point me to the front O2 sensor. :wink:

Bobby...
 

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Never had a backfire, and I haven't noticed any drop in engine response. my tailpipe does have some soot, but i also sit in a lot of D.C. traffic on my daily commute

I cleared the codes last night, and if the CEL stays gone for enough miles for me to pass inspection, i'll be in good shape.

Otherwise, after reading many other related threads on the forum (many of them featuring your insight!), i'm leaning towards trying a new front 02 sensor and the $5 fix for rear.

will check for exhaust leaks while i am doing the sensors, and if the CEL persists at least i'll have narrowed down some of the potential causes.

i can swallow replacing the Cat if i can at least rest assured that i've exhausted my other other options...

thanks again for the input, everyone. will keep you posted.

JB
 

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The Modfather
2016 BRZ Limited - Manual 6 Speed Manual
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One quick and dirty way to check for leaks is to start the car and with a gloved hand cover the tail pipe and listen for hissing where a leak is. The best way of course is to get a very bright light and inspect the exhaust system front to back looking for carbon marks. Regardless change the front sensor to get better MPG's :) I suggest not using a universal one but try to get one you don't have to cut the harness but comes with the plug already on. The universal sensors seem to be hit and miss as far as working properly. As mentioned the front sensor being bad may be causing the rear one to read out of spec. First replace the front and see what shakes out. No point in causing extra work for yourself :)
 
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