Front A/F Sensor and MCU - Related?
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This is a discussion on Front A/F Sensor and MCU - Related? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Recently, my completely stock '02 WRX wagon threw a CEL (P0031 code) at 50,500 miles. I cleared the ECU (disconnected ...

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    Front A/F Sensor and MCU - Related?

    Recently, my completely stock '02 WRX wagon threw a CEL (P0031 code) at 50,500 miles. I cleared the ECU (disconnected battery for a few hours) then (took a shot) replaced the front A/F sensor with a Bosch universal sensor. After installation, the CEL is still up. Frustrated and out of patience, I took the car to a local (non-dealer) Subaru mechanic. After a day of testing all relevant circuits, I was told that the ECU needs to be replaced.

    I've heard some stories about blown A/F sensors damaging the ECU, how probable is it? In addition, is it possible that my universal A/F sensor damaged the ECU? This little CEL will cost me $1500 when all is said and done.
    Last edited by All Pau; 10-10-2007 at 04:35 PM.

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    Did they try to toss in the correct 02 sensor?
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    They haven't yet, but I'm told that the ECU is not communicating TO the A/F sensor, but the A/F sensor is communicating to the ECU.

    Either I'm being taken for a ride, or that $60 universal sensor blew out the $700 ECU. I hear that ECU failures in Subies are extremely rare. I feel like an a-hole. My do-it-yourself nature and desire to save money will actually cost me much more in the end.

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    Quote Originally Posted by All Pau View Post
    They haven't yet, but I'm told that the ECU is not communicating TO the A/F sensor, but the A/F sensor is communicating to the ECU.

    Either I'm being taken for a ride, or that $60 universal sensor blew out the $700 ECU. I hear that ECU failures in Subies are extremely rare. I feel like an a-hole. My do-it-yourself nature and desire to save money will actually cost me much more in the end.
    Either go to your local dealership, PM AnnapolisSubaru on this site or nasioc, or google Genuine Subaru Parts website and buy the proper sensor from Subie Gal.

    Toss that in and see if it fixes things or not. I'd do that before buying a whole other ECU if you are having doubts.

    If you speak with them they might even accept to offer it as a return if it does not fix your issue.
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    Just researched a lot on this CEL last weekend when it popped up on my '02 wrx sedan. I remember reading somewhere that generic sensors like the one you got will not work. I ended up shelling out $200 at the dealer to get the part. It's $150 + $20 shipping at subaruparts.com, but I just payed the extra money at the dealer so I could get it done that day. It's classified as an air fuel sensor at subaru, and an "oxygen sensor before the cat" at autozone and such, but just get it at the dealer. I highly doubt the universal sensor could "break" the ecu - I would think the worst it could do is feed it the wrong data. Hopefully you should be able to just throw it in, reset the ECU, and be good to go.

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    In the end, installing that universal A/F sensor cost me $770 in labor and parts. Before the ECU was replaced, I instructed the tech to install the OEM sensor. Go figure, CEL disappeared.

    Clearly, there is a price to pay for stupidity. I just blew $500 in labor charges looking for a ground fault that originated in that Bosch universal sensor. Trying to save money just cost me, bigtime.

    Let this be a lesson to everyone, DO NOT USE UNIVERSAL A/F (O2) SENSORS! Spend the additional dough and buy the OEM part.

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    Quote Originally Posted by All Pau View Post
    In the end, installing that universal A/F sensor cost me $770 in labor and parts. Before the ECU was replaced, I instructed the tech to install the OEM sensor. Go figure, CEL disappeared.

    Clearly, there is a price to pay for stupidity. I just blew $500 in labor charges looking for a ground fault that originated in that Bosch universal sensor. Trying to save money just cost me, bigtime.

    Let this be a lesson to everyone, DO NOT USE UNIVERSAL A/F (O2) SENSORS! Spend the additional dough and buy the OEM part.
    Not always...but sometimes Subaru's like Subaru parts.
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    Are their instances in which the universal A/F sensors have performed properly in a Subaru? If it is so, perhaps I won't feel so stupid.

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