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Discussion Starter · #1 ·
Hello. I have a 08 Outback. I tried to get it through emmissions, but it failed. I got the above-mentioned errors. So I bought two new Denso O2 sensors. I installed them, and retried. Same errors. I've checked the new sensors for resistance. And I've checked the voltage coming into them, it's around 12v. What could be causing this error to continue? Thank you for your help.
 

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2008 Subaru Outback Ltd
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Did you clear the codes? If not, then the errors will not go away until specific drive times are complete. Remember, clearing the codes will require the same drive times to verify that the new O2 sensors are working properly. In either case, you cannot make a trip to the testing station for at least a week.

A typical scanner will let you know when the O2 sensors have passed their tests.
 

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Discussion Starter · #3 ·
I didn't clear the codes. I just thought the new sensors would be functional, and the error would not be generated. I guess I'll have to give it some time. Thank you. Another thing that I didn't mention is that when I went back I got a third error. A P0420. I didn't mention it because I thought it was info just like the info from the other 2 errors. But I've been finding that this error usually means that I need a new CAT. Is this usually the case? Thank you.
 

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The P0420 is a warning. Personally, I would clear the codes and monitor the 'ready' status on a weekly basis via a scanner. I can't stand to drive when the check engine light is on.
 

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Meh.
I has wagons.
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Any autoparts store will clear them for free...presuming you live in the US and not California. You don't say.

And the P0420 is almost never the cat. Search here on the forums.
 

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2008 Subaru Outback Ltd
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Autozone does not clear codes. Other parts stores may lend you a scanner for parking lot use, then you can delete them.

The brute force method to clear codes is to disconnect the battery ground for 10 minutes. Also a good time to clean the battery posts.
 

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Meh.
I has wagons.
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12,348 Posts
Autozone does not clear codes. Other parts stores may lend you a scanner for parking lot use, then you can delete them.

The brute force method to clear codes is to disconnect the battery ground for 10 minutes. Also a good time to clean the battery posts.
Since when? Everywhere does around here.
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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Since when? Everywhere does around here.
At least in Ohio, clearing the codes is considered tampering with the emission control system if you are not a licensed repair facility and is not allowed. That, and AutoZone was sued for allowing this to happen. No employee should be clearing the codes.
 

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Meh.
I has wagons.
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12,348 Posts
Well then.

No emissions testing in TN, so all the AutoNAPAAdvanceReillys will read and clear codes.
 

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Those sensor codes will remain in memory for up to 40 drive cycles even though the problem has been corrected. (They are automatically cleared after that.) More immediately, if the problem is corrected, the CEL will normally remain on for three consecutive drive cycles without any detected fault, and then go out. (The stored codes remain as noted previously.) However, if any other fault is detected, such as the P0420 in this case, even if the sensor fault were correctly resolved by the new sensors, the CEL remains on, and any time the codes are read, they will all show up (for up to 40 cycles).

It's somewhat unusual for the heaters in both sensors to fail at the same time, and if one had failed earlier, that alone should have led to a CEL. This could raise some doubt as to whether replacing the two sensors has, in fact, resolved the faults causing the two original codes, and the codes might be remaining active because the fault is still there.

Consequently, clearing the codes and then seeing what comes up afterwards makes sense.

Also, if the old sensors are still available, perhaps measure their heater resistances. (If they're Densos, it's probably the two black wires.) They should be in the 2 -5 Ohm range. If they are bad, then there's a good chance the new ones are fine. But if the heaters are still good, then the original cause of the two codes was probably something else.

In this regard:

I've checked the voltage coming into them, it's around 12v.
Where exactly did you measure the voltage?
 
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