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post #1 of 13 (permalink) Old 11-16-2012, 05:16 PM Thread Starter
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OBDII codes

99 legacy outback 2.5, 235k, recent new head gaskets, original catalytic converter,
have a replacement autozone gascap, that has been in use for prior 3 months, without any codes
after the HG, got a P0420 followed by 2 PO440's, so there are currently 3 codes in my obd reader, listed as fault 02 and pend 01

P0420 Catalyst Efficiency Below Threshold (Bank 1)
P0440 EVAP Emission Control System Malfunction

Thinking gas cap probably ok since no codes since I replaced it a while ago, and probably next step go to smog check place to see if their analysis shows I have a bad cat converter.
Any other ideas to try?
If bad cat converter suggestions where best to get a replacement?
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post #2 of 13 (permalink) Old 11-16-2012, 06:48 PM Thread Starter
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P0420 Catalyst Efficiency Below Threshold (Bank 1)

just realized the 'bank 1' indicates the code is coming from the passenger side head where no 1 cylinder is. if there is a bad cat converter, would it not affect all the cylinders and end up putting out codes for both heads?
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post #3 of 13 (permalink) Old 11-16-2012, 09:45 PM
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Most likely a failing oxygen sensor or exhaust leak.

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post #4 of 13 (permalink) Old 11-16-2012, 10:29 PM Thread Starter
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ohhhhhh I hope your right

of course that assumes an o2 sensor is less costly than a new cat converter!
I will trouble shoot for obvious o2 sensor stuff, but if they other wise looks ok, is there any way to test it w/o an oscilliscope? all I have is a decent VOM
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post #5 of 13 (permalink) Old 11-16-2012, 10:48 PM
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Quote:
Originally Posted by bbxrider View Post
just realized the 'bank 1' indicates the code is coming from the passenger side head where no 1 cylinder is. if there is a bad cat converter, would it not affect all the cylinders and end up putting out codes for both heads?
Keep in mind that many error codes are SAE specified- meaning generic to all makes and models. Pretty sure the 0420 is among them, like all 0xxx codes. Bank 1 would indicate one side of the engine *where applicable* as on a car with separate exhausts for each head. With a merged exhaust like the Subaru, it is simply the default.


You have a bad O2 sensor, a leak in the exhaust, or a bad cat- in order of likelihood. Possibly more than one problem.

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post #6 of 13 (permalink) Old 11-17-2012, 08:21 AM
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As mentioned, P0420 seems to be a generic code relating to a number of possible causes. cardoc has started an informative thread about this: http://www.subaruoutback.org/forums/...ght=P0420+diag
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post #7 of 13 (permalink) Old 11-17-2012, 09:18 AM
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I read cardoc's p0420 thread last night. Totally in awe- very thorough. strongly suggest the OP runs off to read it.

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post #8 of 13 (permalink) Old 11-28-2012, 11:20 PM Thread Starter
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testing the front O2 sensor

finally got a plug for a test harness and also needed a new DVOM. After reading a number of posts about testing sensors I tried to test sensor while its installed in the front cat. But see pic, the readings just don't make any sense. It seems the front sensor is ok, based on the way I'm reading the codes. Again I have both a p0420 and p0440, when I disconnect the front sensor I get a p0135 which goes away when I reconnect it. My reasoning is if the front sensor was bad it would cause the 420 and 440 so disconnecting it for the test would not change the error codes. Again see pic, could the yellow and white wires be the O2 heater, thus no volt readings on them? Could the black be the wire for the O2 readings and thats why it has the braided shield? to 'shield' it from adjacent wire voltages because its so sensitive? Don't really want to take this sensor out for a bench test, have to take apart the exhaust header pipes just to get at it?
I have the shop manual wire schematic for a 99 outback but there are no wire colors on it
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post #9 of 13 (permalink) Old 11-28-2012, 11:43 PM
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P0440 is often as simple as a leaky/loose gas cap. My father gets that code constantly on his '98 because for some reason he can't get it through his head to tighten it until it clicks.

So, it could be totally unrelated to the other code. Never hurts to check the really simple stuff first! I'm sure we all forget to even try the 10-second fixes before diving into some intensive troubleshooting sometimes!

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post #10 of 13 (permalink) Old 11-29-2012, 12:26 AM
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thinking there could be 2 problems as well, wondering if inspecting the fuel filler neck might be a good idea.

but, given the work done, it's very tempting to suspect a vacuum system problem which 'could' cause both codes I expect.

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