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Legacy keeps going through O2 sensors.


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'07 Legacy Limited 2.5i, non-turbo, 140K miles.

 

Since 2011, I have replaced an O2 sensor 5 times. Each time, it's due to CEL and error code P0131. These sensors are supposed to last 100K miles. I drive about 10-12K miles per year. Replacing the sensor does resolve the problem for a year or two (lately more like just a year), but it seems like maybe there's another issue somewhere.

 

Any ideas? The car is properly maintained otherwise, no other CELs, no known oil/exhaust leaks. The sensors aren't coming out filthy or anything. My mechanic told me to just replace the sensor.

Edited by Iltl32
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It sounds like the sensors are failing due to some sort of fouling or an electrical issue.

 

Fouling could be due to a very minor head gasket leak (oil or coolant into cylinders) or something that you might be doing in routine maintenance, like using a sealant or cleaner that is not safe for the sensor.

 

Electrical could be something like a bad ground or other damage to the harness. If your mech has tested the harness and found nothing wrong, it could be a small enough section of wire damage that you might have to strip the loom back to find it.

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He didn't mention a short. My thing is that since replacing the sensor fixes the issue for a year or two, wouldn't that mean it's the sensor itself?

 

I replaced the sensor and the issue is gone again, for now. The old sensor came out with soft powdery black carbon on it, after 2 years and about 20K miles. That's more or less normal right?

 

One thing I forgot about is that I did have an exhaust leak which I had repaired about 6 months ago, and I know exhaust issues can ruin sensors. I wonder if that was a factor.

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I don't have much to add, but somethin doesn't seem right. I voluntarily replaced my oem sensor at around 225k without a check engine light, was trying to troubleshoot mpg that was a little below average (in my opinion. I think dirty maf was the culprit). I've been running an NTK sensor for about 25k now without any problems. Here's my old o2 sensor which looks white without much black carbon, wonder if you're running too rich and that's killing the sensors.

oxygensensor.thumb.jpg.827768894480bae2e0b287883b2f37d1.jpg

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