O2 sensor vs A/F sensor question
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This is a discussion on O2 sensor vs A/F sensor question within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; On my 2003 WRX I got a P0031 code (bloc 1, sensor 1) while traveling at a high rate of ...

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    O2 sensor vs A/F sensor question

    On my 2003 WRX I got a P0031 code (bloc 1, sensor 1) while traveling at a high rate of speed. I replaced the front O2 sensor, checked the fuse and there are no shorts in the wires. After clearing the code after about a minute on warming up the car codes again. While trying to figure out why I keep coding I have discovered that I used a downstream Oxygen sensor where I should have used a Air/Fuel upstream sensor. Although they are basically the same things, could this be causing my continual errors? I haven't cross checked my ohm readings (3.6 ohm if I remember correctly on my new wrong front sensor) with my rear sensor so they could be different and would that make a difference?
    If anyone can offer some insight? I do understand the obvious answer which is that I used the wrong sensor. However they may be essentially the same item. The car has around 100k miles on it. Any insight as to what problem I may have caused initially or if I should cough up the coin and get the correct sensor will be Greatly appreciated!
    Thanks,
    Rich.

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    Moderator Donkey's Avatar
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    O2 sensor vs A/F sensor question

    They are not the same. The front sensor is a wideband that supplies the ECU with AFR feedback data while the downstream one is a narrowband sensor used only for cat efficiency.


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    OMG WTF MainFrame's Avatar
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    What Donkey said, they're not the same at all. The front sensor sends detailed info to the ECU about AFR, the rear sensor just tells if your cat is working or not, basically a pass or fail sensor.

    When replacing the front sensor don't use the generic one, spend the money on a Subaru specific sensor. The generic ones burn out constantly.

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    Donkey, Thanks that is good to know. So my ECU is not getting the info it needs. That explains a lot. Once I figured out my mistake with the sensors it was one of those things that you know has to be the problem but afraid to spend the $$ twice to find out that I could still be wrong. I needed informed information about my error so I wasn't taking stabs in the dark. I will change the sensor to an F/A tomorrow. Changed my plugs today. Old ones didn't look bad so that was a good sign. Thanks again, you have been a big help.
    Rich
    Last edited by riicht; 10-15-2012 at 03:55 PM.

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    Mainframe, Thanks for the info as well. I tend to try to save money where I can but knowing that the El Cheapos burn put easily just makes it more costly so I will go with the Subi.
    Rich

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    Admiral Ackbar the 1st mycologist's Avatar
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    Quote Originally Posted by riicht View Post
    Mainframe, Thanks for the info as well. I tend to try to save money where I can but knowing that the El Cheapos burn put easily just makes it more costly so I will go with the Subi.
    Rich
    This is the OEM one - you don't have to pay the Subaru markup.

    Denso 234-9011 Air Fuel Ratio Sensor : Amazon.com : Automotive
    "From a little spark may burst a mighty flame." - Dante
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    Quote Originally Posted by mycologist View Post
    This is the OEM one - you don't have to pay the Subaru markup.

    Denso 234-9011 Air Fuel Ratio Sensor : Amazon.com : Automotive
    Thanks, just placed my order. $122 plus shipping= $133 a great deal on this part. Up to $220 from parts stores. Even with 2 day shipping it was worth the cost and your link prevented me from compromising quality for cost. Anxious to get the performance back and this problem has been costing me fuel.

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