Question about 1997 Subaru Outback

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I have a 96 Legacy Outback 2.5L with 119000 miles. Lately the brake and battery light have been intermittently coming on and off with an accompanying increase in the brightness of my headlights. I hooked up an OBD2 and got the P0325- Knock sensor circuit malfunction code. Would these two be related? I have a new (within 6 months) alternator and a brand new battery.

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  • cheshirechef Jul 01, 2009

    I will be replacing the sensor this weekend, but I was mostly concerned with the brake and battery lights and the headlights flaring up. How likely it is the changing the sensor will fix this problem as well? Also, what would be the best/easiest way of replacing the sensor? I do have a bit of familiarity with auto work, but not a ton.

  • cheshirechef Jul 01, 2009

    I got the new sensor, had the battery and alternator tested (both are fine) and as soon as the engine cools down, I'm going to head out and work on it. Wish me luck, and thanks for the help! Any other words of wisdom before I begin?



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A Knock Sensor allows the engine to run with the ignition timing as far advanced as possible. The computer will continue to advance the timing until the knock sensor detects pinging. At that point the computer retards the ignition timing just enough for the pinging to stop. A knock sensor assures that you're getting as much power and fuel economy as is possible from your engine.

The knock sensor responds to spark knock caused by over advanced timing. A knock is a sudden increase in cylinder pressure caused by preignition of the air fuel mixture as the flame front moves out from the spark plug ignition point. pressure waves in the chamber crash into the piston or cylinder walls resulting in a sound known as a knock or ping. this is caused by using a fuel with a low octane rating, overheating, or over advanced timing. sometimes it can be caused by hot carbon deposits on the piston or cylinder head that raise compression.

So if the knock sensor is faulty - it sends bad info to the ECM to retar d your ignition. If it is bad enough - the engine will go into an almost "limp home" mode where the RPMs are barely enough to keep the alternator running.

Change the sensor... let it cycle 4 times (hot and cold) then reset the codes.

Thanks for using FixYa!!

Posted on Jul 01, 2009

  • 3 more comments 
  • blueextc3221
    blueextc3221 Jul 01, 2009

    The knock sensor is Under hood, center, rear engine area, mounted on rear of cylinder block below valve cover

    It should take you 20 minutes if you have never opened your hood before today ;D

    One nut holds it in place.... the tricky thing is getting to it.

    You need small hands or a few swivels and extensions. But take your time.

  • blueextc3221
    blueextc3221 Jul 01, 2009

    As far as the CELs coming on - if the sensor is faulty and producing a ground condition... it could affect the way the BCM translates the info.

    With the sensor replaced - and the lights still coming on - chances are the BCM is the second problem you are experiencing. In that case, the entire module is replaced... there is no way to repair.

  • blueextc3221
    blueextc3221 Jul 01, 2009

    While you are at the parts store...even though they are 6 months old.... have the alternator and battery LOAD tested to rule them out.

    It is not unheard of to get a bad battery off the shelf with a dry cell... or improperly wound armatures in an alternator (especially one that is a remanufactured one)

    Most chain parts stores will do it for free in an attempt to sell you the replacement parts.

  • blueextc3221
    blueextc3221 Jul 01, 2009

    a few more pics to help you locate the Sensor on your Subie.....

    PIC 1 pointed to as "B"

    PIC 2 Just to left of the wire harness plug a (and under the hose) you can make out the bolt and sensor.

  • blueextc3221
    blueextc3221 Jul 01, 2009

    No - it is pretty straightforward... just dont overtighten it. :D

    Good Luck... remember - cycle it 4 times.... running temp to cold... then have the codes reset.

    The ECM needs to callibrate to the new sensor.

    Thanks for using FixYa!!



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