What does it mean when the Check Engine light comes on and goes off?

Discussion in 'General Motoring' started by Yousuf Khan, Apr 12, 2010.

  1. Yousuf Khan

    Yousuf Khan Guest

    I got a check engine light come on a couple of days back, and it was
    there for less than a day before it went blank again. I have a car code
    scanner, and it came back as P0325 (Knock Sensor problem). Now the fact
    that the light went out again, does it mean that the knock sensor fixed
    itself? I checked the code again, and it still shows the same code, but
    that's probably just because it records the last problem.

    I know that the Check Engine light sometimes automatically goes out
    after a certain number of days, but I thought that would be after 3 days
    or so.

    Should I clear the code, and see if it recurs?

    Yousuf Khan
    Yousuf Khan, Apr 12, 2010
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  2. Yousuf Khan

    mulder Guest

    It means the problem is being detected intermittently by the ECU. When
    the condition isn't seen for a few driving cycles, the light will go out
    but the code remains in memory for retrieval. If the problem is detected
    again, the light will come back on.
    Most likely the sensor itself is the problem, but it could also be a
    wiring fault. The knock sensor is not an expensive part and is fairly
    simple to replace.
    mulder, Apr 13, 2010
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  3. Yousuf Khan

    Yousuf Khan Guest

    I kind of figured it isn't too hard to fix, as the dealer is only
    quoting 45 minutes for labor on this. However, he's also quoting $160
    for the part! I figure if I have to pay that much for the part, I might
    as well save on the labor by doing it myself.

    Is that as good a price as I'm going to get for that part? It's in
    Canadian dollars, but the US and Canadian bucks are pretty much the same
    these days.

    Yousuf Khan
    Yousuf Khan, Apr 13, 2010
  4. seems high. Regardless, I always price stuff with Jamie at
    www.subarugenuineparts.com and then decide. Sometimes you can get a
    local dealer to match online parts. (this worked for my springs and
    got close enough on my SS braided brake lines to spend the money
    locally. Other stuff, I bought (engine undercover, Roki oil filters,
    STI windshield wipers for my WRX, etc.) from them. There 'may' be a
    Bosch or other aftermarket part - but folks have had bad luck with non-
    OEM for other sensors, knck sensor might be OK aftermarket. YMMV

    1 Lucky Texan
    1 Lucky Texan, Apr 13, 2010
  5. Yousuf Khan

    S Guest

    Hi Yousuf!

    This is quite common.
    And yea, clear the code. It will most likely re-occur, but as long as
    the CEL is goin' away after a day or two, I wouldn't worry about it.
    If it starts staying on for longer periods. you'll want to replace the
    sensor; your gas mileage will suffer otherwise.
    I'd suggest getting one at a salvage yard; probably $30 or so. There
    is a way to test one with an ohmmeter. I don't recall the exact
    procedure, but sou should be able to find it on-line, and the yard
    guys should know in any event.
    It's about a 10 minute job to swap one of these; takes a 12mm socket,
    an ~4 inch extension, a ratchet, and an ice pick or similar to work
    the connector.
    Let me know if you need details.

    ByeBye! S.

    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101
    S, Apr 13, 2010
  6. Yousuf Khan

    Yousuf Khan Guest

    Unfortunately, those guys don't ship to Canada (I've asked already). So
    it's not certain that the dealer is going to try to match the online
    price, if they know that these guys won't be shipping into here.

    Yousuf Khan
    Yousuf Khan, Apr 13, 2010
  7. Yousuf Khan

    Yousuf Khan Guest

    Thanks Steve, I found an online instruction page with pictures showing
    where the knock sensor is and what it looks like (at least for a Legacy,
    might be the same for an Outback).


    Yousuf Khan
    Yousuf Khan, Apr 13, 2010
  8. Yousuf Khan

    S Guest

    Hi Yousuf!

    De nada.

    Legacy, Impreza, SOHC 2.5, DOHC 2,5 all pretty much the same knock
    sensor arrangement; good ol' Subaru. Some models, you may have to pull
    off more of the air intake plastic to get at it, that's about all. I'm
    lazy, and usually just take off everything as a unit, all the way to
    the throttle body; that way everything stays clean and more or less in

    When you put it back on, be sure to re-connect all of the PCV hoses,
    and be careful that the boot at the throttle body doesn't get pinched

    This makes a good time to install a fresh air filter, and PCV valve if
    you're so inclined.

    Have fun!

    ByeBye! S.
    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101
    S, Apr 13, 2010
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