P0325 - Knock sensor fault. Resistance OK, but how does the sensor actually work ??
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  1. #1
    PWCToday Newbie
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    P0325 - Knock sensor fault. Resistance OK, but how does the sensor actually work ??

    Hi Guys,

    New to this forum, and new to Jetski's!

    I took my ski out yesterday, only to find that after a few minutes I got a P0325 error (knock sensor). 2009 RXT IS 255.

    Happy to replace the sensor, but have read a few posts suggesting that replacing the sensor doesn't always fix the issue. Those threads haven't gone on to explain what the issue is.

    I cant find any other threads to really help me move any further.

    A few quick points.

    1) I've tested the wires as per the service manual (both to the plug, and the to ECU), and the resistance is 5Mohms as required.
    2) This morning I started the ski, and surprisingly it was fine. Even revving it up past 5000rpm produced no errors.

    However after a few minutes, the fault code came back. Conclusion - it seems to only happen once the engine warms up.

    My MAPS error that I had taught me one lesson - seadoo error codes are not always related to the actual issue!. Plus ill admit, i love gettong down and dirty with detail!

    I haven't taken the inlet manifold off yet, so I haven't been able to check the wires down lower, but the plugs etc that I can access look ok.

    I haven't checked the mating surface of the sensor to the block yet. However the engine has been freshly rebuilt, and I was very particular as I rebuilt it to ensure that all torque settings were followed, and that the surfaces were clean (that's certainly not to say I haven't mucked it up - but the ski did run fine for the first run after the rebuild).

    Having said that, is the the mating surface really relevant unless there is actual knock? (P0325 doesn't refer to knock perse, it refers to the sensor being faulty).

    Theoretically I would have thought you could unbolt the sensor from the block and just leave it hanging, and all that would result is that the engine would never pickup knock.

    My understanding = The crystals inside the sensor will generate voltage when it vibrates at the correct frequency. This voltage is transmitted through the wires to the ECU which determines how much to retard the engine timing by.

    The factory manual says there should be 5Mohms across the two sensor wires. However I wonder (relatively ignorantly) if that resistance is simply for the ECU to determine if a sensor is actually present?. If it senses no resistance, it assumes there is no sensor connected, and throws an error. In theory, I should be able to unplug the sensor from the main harness, and bridge the two pins in the main harness with a 5Mohm resistor...............hmmmmmmm. Pity I don't have a 5Mohm resistor.

    I realise I'm getting down into the weeds here..........but hoping someone might be able to chime in and tell me if im on the right track.

    Dave

  2. #2
    PWCToday.com Is My Home Away From Home cyrillefrenchy's Avatar
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    Re: P0325 - Knock sensor fault. Resistance OK, but how does the sensor actually work

    i have seen that issue a few times, first i would drain and refill gas tank with fresh high octane and new plugs, if not cured the problem,replace knock sensor and make sure the surface where sensor touches the block is clean ( ground connection) and if still the same then disable knock sensor with BUDS and see if it fixes it, if yes then the ecu is defective, i have seen that case before.
    The Jetski Repair Shop
    South Pasadena Florida

  3. #3
    PWCToday Newbie
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    Re: P0325 - Knock sensor fault. Resistance OK, but how does the sensor actually work

    Hi guys I thought I had replied to this with my fix.....sorry.

    This turned out to be faulty wiring in the harness. Not the knock sensor wiring but the harness.

    There is an earth wire running to the knock sensor plug that is “un shielded”. Similar to how a coax cable looks inside.

    Water has gotten inside this part of the loom and corroded the earth wire completely.

    Sorry......I didn’t take a photo.

    I replaced this part of the loom and problem resolved.

    Dave


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