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Catalytic Convertor


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IIRC federal regulations require the oem cat as a replacement no other. This is why shops mostly won't replace a cat with a universal one.

 

Now if you take a car with no cat in they can put one in place no problem.

 

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I don't remember the exactly rules off the top of my heads. To the letter of the federal law tampering with catalytic converter is pretty strict and you need a OEM or certified OEM like replacement (I want to say this is 60k miles or less)

 

In past, I have used universal replacements and high flow cats. Unless your state is a smog nazi state that is going over your car with a fine tooth and comb it shouldn't be an issue. 2.5i Legacy isn't likely to raise an flags either. In the past on my Corvette and Syclone, the inspection station has sometimes checked to make sure my clearly aftermarket catalytic converter wasn't hollow. My Corvette was actually missing the precats with my aftermarket headers. My cars pass the sniffer/dyno load testing so that is all they cared about. (MA has since dropped the sniffer/load testing) I would have had an issue in CA in the counties where they do through visual inspections.

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I have had code 0420 on other cars. The reason it take some miles for the code to reappear is that ECM has to detect the condition for 3 times in row. In my case of my 3 cars, the rear O2 sensor was faulty in everyone of them. 2 of the cars were just over 100k, the other was 125k miles.

 

 

 

Someone needs to diagnose the issue. Advantage Auto parts isn't. Looking at the Subaru diagnostic table, most of the diagnosis is either data logging and looking at the rear O2 sensor wave form or using multimeter to check continuity and resistances.

 

 

 

Subaru is who diagnosed it the 2nd time. They never mentioned the 02 Sensor maybe causing the issue. It very well could be, though.

 

 

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I say put in a new rear o2 sensor. That would explain the bad gas mileage. The ECU isn't getting the proper reading from the o2 and it thinks its lean, so it's telling the injectors to add fuel across the board in all RPM and load conditions.
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I say put in a new rear o2 sensor. That would explain the bad gas mileage. The ECU isn't getting the proper reading from the o2 and it thinks its lean, so it's telling the injectors to add fuel across the board in all RPM and load conditions.

 

wouldn't that be the front O2? that is the AFR sensor. the rear is just a narrow bad cat efficiency sensor. that shouldn't have much effect on MPG.

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wouldn't that be the front O2? that is the AFR sensor. the rear is just a narrow bad cat efficiency sensor. that shouldn't have much effect on MPG.

 

You may be right and I may have them mixed up.

 

OP, what code were you getting?

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Front sensor/s on recent/current-gen Subarus are 'bastardized' widebands (read ~ accurate down to about 11:1, nothing lower) are are referred to as 'AF Sensors' or 'Lambda sensors' (Bank 1, Sensor 1 on H4s plus Bank 2, Sensor 1 on H6s).

 

The rear sensor/s are the old-school narrow-band 'O2 sensors' and yes, mainly used to monitor cat healthy/efficiency BUT on all recent Subarus (say 2005+) they DO have an impact on fueling contributions (and hence A/F errors).

 

You can see how your O2s are impacting fueling by monitoring/logging:

 

'AF Learn #3" and 'AF Correct #3" for H4s

plus

'AF Learn #4" and 'AF Correct #4" for H6s

 

Add these up (per bank of cylinders) with your #1/2 learn/correct readings to get a true representation of fueling corrections (really just an effect on Injector PWs).

 

For anyone looking to replace stock cats with something aftermarket and a tad cheaper (but still OBD-II and EPA/CARB, Cali-emissions compliant), best to go with GESI units (branded by Vibrant but produced in Canada by GESI).

 

http://www.vibrantperformance.com/catalog/index.php?cPath=1527_1326

 

You can typically get them far cheaper if you shop around online (Jegs, Autoplicity, THMotorsports, CarID, TunerSports)

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Just wanted to update and say that it is indeed a O2 sensor. After reading about the ‘Bank 1,’ code, I ruled it out and it did solve the problem. You guys are awesome! My bank account and myself are very grateful

 

 

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  • 2 years later...
Just wanted to update and say that it is indeed a O2 sensor. After reading about the ‘Bank 1,’ code, I ruled it out and it did solve the problem. You guys are awesome! My bank account and myself are very grateful

 

 

Sent from my iPhone using Tapatalk

 

Resurrecting a really old thread. I have a similar issue. Looking for confirm if replacing the front vs. the rear O2 sensor is the way to go?

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Depends on the problem- what code(s) are you seeing? If it's something related to the catalytic converter, the rear sensor would more than likely be the one to change out.

 

Same issue as the OP, P0420 code comes in intermittently. More frequent when the weather is cold.

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Same issue as the OP, P0420 code comes in intermittently. More frequent when the weather is cold.

 

Replacing the rear O2 sensor got rid of my 0420code. It's real easy from the top of the engine bay too!

 

If you have the GT, the only real fix is to get a J pipe and delete the rear O2 sensor...;)

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Same issue as the OP, P0420 code comes in intermittently. More frequent when the weather is cold.

 

Connect up a OBDII scan tool and look at the rear o2 sensor data. If your cat has truly failed, one would expect the rear o2 to follow the front o2 sensor (lean to rich to lean to rich.....)

 

I just did both rear o2 sensors on my 2010 outback 3.6R because the passenger one was totally wacked out in what it was showing for output... once I put the new sensors in, the p0430 went away (same as p0420 on the 2.5L)

 

as soon as I put the new sensors in and got the car in closed loop, the voltages were stable and this shows the CAT working

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