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Discussion Starter #1
Hi


Im wondering if someone can help me.


I've just got the P0420 error on my 2008 outback and after some reading the first things to check from what i've read are the oxygen sensors and pcv valve.


Please could someone tell me where the sensors and the pcv valve are located.


Thanks
 

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2.5 liter non-turbo engine?

There's two sensors, one just before, and one just after, the front catalytic converter (at the front, right side, under the engine). Look down between the radiator and the engine to the top of the exhaust. (Better to remove the air intake duct.) The sensors are screwed down into the exhaust pipe and have wires coming away from them.

The PCV valve is located on the right side engine block, toward the back, below the ignition coil.

Other than checking the wiring to the sensors, I'm not aware of any simple way to check them. In the absence of more sophisticated scanning tools that can read the signals from the sensors, I think many of the posts suggest changing them.

The PCV valve can be checked for clogging, but once it's removed (to check it) , it might as well be replaced with a new one.
 

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Discussion Starter #3
Thanks for the reply

I think i've narrowed it down to the front sensor. (no output when heated up on the bench)

Unfortunately no one seems to stock them here in the uk.
 

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Does anybody have the wiring info for them, from what i've read on the net the wiring is:

blue: signal +
white: signal -
black: heater +
black: heater -

Can someone please confirm this.

I was thinking of putting a universal one on.

Thanks
 

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Ah, location is U.K.

Schematic for North American 2008 2.5 non-turbo model is attached. Your U.K. version, which is made in Japan, could be different.

In the schematic, signal wires are blue (L) and pink (P), and heater wires are white/blue (WL) and yellow/blue (YL).

Lots of discussions here about code P0420.

As I recall, most recommend using only a genuine Subaru front a/f sensor.
 

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Discussion Starter #6
Thanks for the diagram.

I think i can confirm that the wiring i posted is correct (which is on the sensor to the connector). After bench testing the sensor with a blow torch again, (blue signal + white signal -). I got some readings when i wiggled the cable in the middle, which lead me to believe a broken wire.



I've just got to work out how to clear the ecu codes, because i dont think my ecu clears them once the fault has been fixed (started car up with mass airflow sensor disconnected, re connected it & started the car up again & it didn't clear the codes from that!!) so at the mo i cant check if my rewiring job on the oxygen sensor has worked.

I dont what to disconnect the battery because the stereo just comes up with security on the display & had to be re enabled by the dealer!!. (thats gonna be another thread)


I have a usb OBDII interface is there any free software that will wipe the ecu fault codes?


Thanks
 

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In most cases, CEL fault codes are not cleared when the fault is repaired. Rather, the CEL will remain lit until several (usually three) consecutive full driving cycles are run without a fault being detected, after which the light will go out. The stored code itself, however, will remain in memory for up to 40 drive cycles, or until the memory is cleared manually.

I have a usb OBDII interface is there any free software that will wipe the ecu fault codes?
There's a program called FreeSSM that some of us have used to monitor engine and transmission parameters. I believe it should be compatible with your U.K. 2008, and should be able to clear the ECU codes it finds.

For more info look at http://www.subaruoutback.org/forums...426-freessm-complete-access-your-ecm-tcu.html. It's a rather long thread now but I think worth the read if you are into doing repairs on these more sophisticated systems. The earlier posts have links to the program web-sites. Also there are comments regarding which USB interfaces should work.

I'm surprised that a "no signal" fault related to the a/f sensor is triggering a P0420 only. I would expect there to be other codes as well, in the range of P0131 - 134 and perhaps others.

And again, I'm basing this on the North American version and recognize that there could well be differences in the others.
 
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