how to check an up stream oxygen sensor?
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This is a discussion on how to check an up stream oxygen sensor? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Having an issue... Threw a PO031 code. Ran over a piece of semi tire a few days ago and my ...

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    Question how to check an up stream oxygen sensor?

    Having an issue... Threw a PO031 code. Ran over a piece of semi tire a few days ago and my check engine and all the other pretty lights started flashing immediatly. Drove it for maybe 2 days and it started to freak out on me when I got on the gas in a fun little round about..then it died..started immediatly...give it gas..dies again..parked it. Scanned the codes and I get a misfire on 3 with the PO031 code. Did some reading and tracked down the part at autozone. Replaced the upstream sensor.. code is still there. Won't clear and still drives like ****....any ideas? Are these sensors testable with a volt meter/ohm reader? Voltage at the wiring harness? Anything would help.
    Car is an 08 WRX with 61k miles, Cobb downpipe, magnaflow exhaust,recently rebuilt VF52 turbo(by me), and a forge BPV.

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    The cylider misfire cleared and hasent come back. My MPG went from 24 down to 18. It will rev by it self..sitting at 500 it will rise to 1500 or so..then go back down to 500..repeating it self.

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    After hitting the tire did you inspect the car for any possible damage?

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    Car looked normal.. update.. got a brand new sensor.. 250.. put it in.. clear code and it comes back immediatly. Can anyone tell me the voltage at the plug and which wire it is?!

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    OMG WTF MainFrame's Avatar
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    The voltage is dependent on AFR.. if it was still daylight out I would go check for you, but it's not. I'll try to check in the morning.

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    It would be much appreciated if you remember. Cold or hot start either way just gotta tell me. Lol.. if you know the plug it shouldn't take but 2 minutes. Just unplug it, then prime the car with out starting it. Their are 4 wires to that plug. I can't remember the harness wire colors but I took my voltage readings off the un pluged upstream O2 sensor on the wiring harness. the wires on the sensor are 2 black 1 white and 1 blue. I'm getting voltage at the blue and white wire locations. If you can tell me your readings it would help greatly.

    Also, someone made me aware that the heater circuit that's apart of the sensor has its own relay and fuse and that they can blow. Any idea's on location? I've read under the glove box. I won't be near my car till tonight or I would look.
    Last edited by wuzup76020; 11-21-2012 at 06:46 AM.

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