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Old 08-03-2005, 04:34 PM   #1
brianecarlson
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1999 Outback Limited
Winestone

Default Check Engine Light: CODE P0420

Does anyone know what this code means or what needs repaired:

PO420 Catalyst System Efficiency Below Threshold. Bank 1

Thanks!

Brian
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Last edited by brianecarlson; 08-03-2005 at 04:41 PM.
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Old 08-03-2005, 04:52 PM   #2
fibuz
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From what I've read its either an 02 sensor or your cat is bad...

fibuz
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Old 08-03-2005, 05:19 PM   #3
brianecarlson
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What is the "CAT" or "Catalyst"?
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Old 08-03-2005, 05:22 PM   #4
fibuz
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catalytic converter...part of the exhaust.
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Old 08-03-2005, 08:11 PM   #5
bheinz57
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That's you rear (second) O2 sensor saying the convertors are not doing their job. Have you done any exhaust mods? That is a frequent code for people that have aftermarket headers/exhaust parts. There is a couple ways to fix it if it is due to aftermarket stuff. Otherwise, depending on warranty, let the dealer help you. Brian
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Old 08-03-2005, 09:09 PM   #6
brianecarlson
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I haven't done any mods at all. I"ll take it to my "Authorized Subaru Dealer" tomorrow. Thanks for the advice.
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Old 08-05-2005, 08:20 PM   #7
leonbmx
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I have the same problem... However i did put on GReddy Evo2, GT spec II headers w/ catless UP and Daddy's SCP high flow catted DP...

I bought an ODB2 scanner and got rid of it that way, but is there another way?

Thanks,

leon
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Old 08-16-2005, 01:55 AM   #8
Peaty
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Old 08-29-2017, 09:35 PM   #9
WindyCityYinzer
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Default Resistor Fix

So pulled the P0420, tried the Resistor bypass, but now its pulling P0137 for low voltage. Anyone try this, and have a similar result?
2005 Outback 2.5i
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Old 10-04-2017, 02:21 PM   #10
amiexploited
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^^^^
Dealing with this too, same 2005 Outback but the CA emission one (profile probably doesn't say it)
I'm the last one to post on the http://www.subaruoutback.org/forums/...nosis-126.html and haven't gotten any responses.

Starting around 2005 you can't use the spacer for the rear 02 sensor.

@brianecarlson
any luck at the dealer? I know they will just wire that the cats need to be replaced when the code pops up instead of solving why it popped up.
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Old 10-04-2017, 02:56 PM   #11
Charlie-III
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Quote:
Originally Posted by WindyCityYinzer View Post
So pulled the P0420, tried the Resistor bypass, but now its pulling P0137 for low voltage. Anyone try this, and have a similar result?
2005 Outback 2.5i
Quote:
Originally Posted by amiexploited View Post
^^^^
Dealing with this too, same 2005 Outback but the CA emission one (profile probably doesn't say it)
I'm the last one to post on the http://www.subaruoutback.org/forums/...nosis-126.html and haven't gotten any responses.

Starting around 2005 you can't use the spacer for the rear 02 sensor.

@brianecarlson
any luck at the dealer? I know they will just wire that the cats need to be replaced when the code pops up instead of solving why it popped up.
Sometimes you get that code with an exhaust leak near the rear O2 sensor, so check for leaks first.
If you have a scanner that does realtime data, check activity of the rear sensor, ideally they are at 0.5VDC, lower voltage is lean, higher voltage is rich.
Engine running, change RPM's by a lot, should see the voltage change.
If it's pegged at 0 or 1, likely a sensor issue. Exhaust leaks usually make the voltage go below 0.5VDC.
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Old 10-04-2017, 10:05 PM   #12
amiexploited
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Thanks for the reply. I'll check for exhaust leaks this weekend.
My rear 02 averages at 0.6V during acceleration. The middle 2 are around 0.8V and 0.7V. At idle the rear is at 0V. Voltage changes with throttle. all drop when I let go of the throttle.

Do you have experience reading logs? I have 2 one at idle and one at steady 70mph.
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Old 11-18-2017, 09:29 AM   #13
jagoulet
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Default current thinking?

I own a 2009 Impreza with base, normally aspirated motor. Has 103K miles. No modifications, exhaust system and sensors original.

Car runs fine but PO420 has come on twice in recent months. Gas mileage might be down a tad, not sure (wife's car).

When you guys say you are "logging data" what are you using for a tool to do this?

What is the current thinking on this problem? For example, should I replace the rear O2 sensor as a starting point? I realize they age. Exhaust leaks? can't hurt to look.

Of course the inspection sticker is due to expire the end of this month . . .so motivation to get on with it.

Any thoughts appreciated!

John - MA
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Old 11-21-2017, 12:47 PM   #14
Charlie-III
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Silver Sleeper BK, 5MT

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Quote:
Originally Posted by Charlie-III View Post
Sometimes you get that code with an exhaust leak near the rear O2 sensor, so check for leaks first.
If you have a scanner that does realtime data, check activity of the rear sensor, ideally they are at 0.5VDC, lower voltage is lean, higher voltage is rich.
Engine running, change RPM's by a lot, should see the voltage change.
If it's pegged at 0 or 1, likely a sensor issue. Exhaust leaks usually make the voltage go below 0.5VDC.
Quote:
Originally Posted by jagoulet View Post
I own a 2009 Impreza with base, normally aspirated motor. Has 103K miles. No modifications, exhaust system and sensors original.

Car runs fine but PO420 has come on twice in recent months. Gas mileage might be down a tad, not sure (wife's car).

When you guys say you are "logging data" what are you using for a tool to do this?

What is the current thinking on this problem? For example, should I replace the rear O2 sensor as a starting point? I realize they age. Exhaust leaks? can't hurt to look.

Of course the inspection sticker is due to expire the end of this month . . .so motivation to get on with it.

Any thoughts appreciated!

John - MA
Check for leaks first. Cheap test is get the front up, start engine, have someone use a rag or heavy gloves to block the exhaust tip/tips while you go under the car and listen/feel for leaks. Exhaust tip blocked off makes even small exhaust leaks stand out.
If that is OK, then do downstream O2. Based on age, it may just be tired.
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Old 11-28-2017, 06:56 AM   #15
MyLongForeskin
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Just ohm test the O2 snsr.
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Old 12-11-2017, 05:08 PM   #16
shaunm1311
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Default P0420 with hesitation at acceleration

Ive searched a lot for anyone who has had the P0420 code with actual performance symptoms as well. I own a 08 2.5i NA completely stock, got the P0420 code 2 months ago with no performance issue, as of the last few days I have a hesitation at take off and low rpms. Does the performance issue help narrow down whether or not its a sensor or cat? any help would be appreciated thanks.
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