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Old 11-01-2012, 09:53 AM   #1
afohlin
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Default Can't get rid of P0420

I've had an invidia turboback exhaust for 2 years now and it used to throw a p0420 every once and a while and go off, but now I can't get rid of it. I have a catted downpipe and did the mechanical fix where i drilled one fouler out and screwed them both into the downpipe but it still throws a code. I just replaced the rear 02 sensor since I figured it could have actually been a bad sensor but it wasn't the case and the CEL came back on after a day. I live in Mass and need to get it inspected. I have a friend that has an obdII scan tool but he said if he clears the code it will show up during inspection and it still won't pass. I would rather not pay for a tune since I plan on getting a new car after this winter, and I am nervous about open source tuning it myself. Is there anything else I can do besides find someone who has a working stock turboback laying around and bolt it in to get it inspected? Thanks
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Old 11-01-2012, 10:11 AM   #2
tommyson01
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The easiest and best way to get rid of the code is what you don't want to hear/do. A tune can fix this.
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Old 11-01-2012, 10:14 AM   #3
Bo0stin5STI
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Well, as previously stated, you will need some sort of EM to eliminate it.

Why don't you look into a used AP? Maybe even a V1 AP? Should be a cheap pickup and can be easily sold after your car is sold....or you can up the selling price of your car and throw that in there!

Just my .02
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Old 11-01-2012, 12:04 PM   #4
masterforce
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Get a longer fouler so it get less exhaust. Looks like its still too close and it triggers CEL
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Old 11-01-2012, 01:18 PM   #5
rob1n1
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Ask around in your local forums if you can borrow a Tactrix cable and flash a e-tune on there. That's as cheap (but still good) as you can get. Just tell your e-tuner to make sure P0420 is off.
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Old 11-01-2012, 03:54 PM   #6
afohlin
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I guess I'm a little confused. What is the difference between using an OBDII scan tool and clearing the code and getting a tune to get rid of the code? With a tune will it never read the code again? And if thats the case can I just get a plug for the o2 bung and not run an o2 sensor at all?
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Old 11-01-2012, 05:02 PM   #7
Bo0stin5STI
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The tune with AP's turn that code and a few others "off" so they can't come on again.

The issue with not running o2 sensors is the fact that the car uses all inputs to correct fueling/AFR along with others. Not running the sensor can cause "lean"/"rich" conditions.

Leaner is meaner but closer to destruction!
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Old 11-01-2012, 05:02 PM   #8
rob1n1
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Default

Quote:
Originally Posted by afohlin View Post
I guess I'm a little confused. What is the difference between using an OBDII scan tool and clearing the code and getting a tune to get rid of the code? With a tune will it never read the code again? And if thats the case can I just get a plug for the o2 bung and not run an o2 sensor at all?
You can use the scan tool to clear it, but that's only until it comes up again.

You don't need a full "tune" per se, but you can go into the ECU and turn that code off. As in, never comes up again, and will never be a problem for you. This is a common thing to do with a stage 2 tune (I know I had to turn mine off) as the high-flow performance cats that all the aftermarket exhausts use will likely throw it one way or another.

I believe you can just go without the O2 bung, but I'm not 100% on that. Hopefully someone else can chime in on that.
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Old 11-16-2012, 05:42 PM   #9
krause415
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afohlin,

I've got the excate same problem. We both live in states where emissons are required. I've recently learned both the anti foulers and tuning are illegal for non track cars.

You can get a tune done which will knock out the code depending on if the tune shop will do it for you.

I'm now looking at getting a COBB catted down pipe , my hope is that I dont need to get subaru's and can get aftermarket and pass emissons. My good news is after replacing front O2 is that with a drive cycle I got a cel for the good ol p0420 code.

My .02 .. It all depends which way you are willing to lean
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Old 11-16-2012, 07:39 PM   #10
Pandasaurus_rex
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Quote:
Originally Posted by Bo0stin5STI
The tune with AP's turn that code and a few others "off" so they can't come on again.

The issue with not running o2 sensors is the fact that the car uses all inputs to correct fueling/AFR along with others. Not running the sensor can cause "lean"/"rich" conditions.

Leaner is meaner but closer to destruction!
As far as I know, the rear o2 sensor is only used for emissions detection. The front o2 is used for closed loop fueling, which affects afrs in cruise and light load.
The op should try stacking another non-fouler underneath the other one. I'm running catless, and the dp bung is as long as 2 non-foulers stacked together. I've never had a code thrown.
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Old 11-17-2012, 04:54 PM   #11
belair0607
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Default Same problem

2005 Forester X. Anybody around Nashville that can help out with the program delete?
Did spacers before reading that it will only trade the P0420 for another lean condition code on 2005 and up. Passed emissions testing easily.
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Old 11-17-2012, 04:56 PM   #12
belair0607
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Default 2005 and up

Rear O2 sensor gets into the tuning game.
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Old 11-17-2012, 06:49 PM   #13
Jack
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Call Bren from Brentune and ask him. He's close enough to you and he might be able to do it inexpensively. He works out of a small place at the intersection of 20 and 122 in Worcester.
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Old 11-17-2012, 07:06 PM   #14
AlucardFD
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Bren used to etune my car, cool guy.
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Old 11-17-2012, 09:16 PM   #15
mod maniac
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Default

On the op's car you can weld the hole closed on the antifouler and it won't throw that code or you can hang the sensor under the car and plug the hole. Ether way will work but don't do it on an 05 or newer.
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