2007 Impreza stops for no reason

Discussion in 'Subaru Impreza' started by blank, Nov 15, 2009.

  1. blank

    blank Guest

    Driving along the highway and the car just stops for no known reason. It
    happened three times on a long trip recently. Had cruise control turned on
    at the time but this might be just a red herring. Can put it into neutral
    while still moving and turn the key and it restarts. Have had intermittent
    trouble with this vehicle since new--sometimes it just wont start. Grind
    and grind away at it and it goes. I think it is some sort of electrical
    problem but am just guessing. Any thoughts?
    blank, Nov 15, 2009
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  2. blank

    JD Guest

    I'd look at the ignition module. Intermittent faults are notoriously hard
    to diagnose.
    JD, Nov 16, 2009
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  3. blank

    blank Guest

    Yes, I can imagine that it is going to be more or less impossible to find.
    If the fault is not showing how can a mechanic know what to fix? I guess we
    will just have to live with it, but its a real disappointment--it means we
    need to change our thinking and realise that we can not consider the car to
    be reliable. Damn.
    blank, Nov 16, 2009
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    JD Guest

    There are a few things you can try that aren't expensive. I would change
    the plug wires, and check the connections to the ignition module, including
    the ground. They can test the ignition modules. Also, does the car throw a
    code when it happens?
    JD, Nov 16, 2009
  5. blank

    blank Guest

    I wasnt aware of any code display. Didnt notice anything at the time. But
    we were so freaked out by it happening that I could have missed it.
    On one occasioin we were in very hilly singlelane each way conditions out in
    the middle of nowhere in the region of Mt Isa, and I knew there was a huge
    roadtrain close behind me because I'd just passed it, and the bloody thing
    concked out. I nearly shat myself. Anyway got it going again before being
    crushed by the roadtrain. If my wife had been driving at the time it might
    have been a very different story.

    OK, so where does the code show up? When they test the ignition modules
    would an intermittent fault like this be diagnosed? Appreciate any comments
    before I take it to Subaru.
    blank, Nov 17, 2009
  6. blank

    S Guest

    Hi Blank!

    '07 car is (should be, anyway) still under factory warranty. I'd take
    it back to the dealership and make it _their_ problem.

    On a vehicle this new, the most likely candidate IMO is an
    intermittent in the wiring harness.

    Start the car, stand on your head so that you can reach up behind the
    dash, and start moving wires around. Pay particular attention to the
    large bundle(s) that terminate at connectors thru the fire wall. When
    you move the bundle that has an intermittent. in all probability the
    engine will hiccup, or stall. Spread the wire bundle and start again,
    moving individual wires until you find _the one_.

    My reasoning is this:

    When the wiring harness is assembled, the connector male and female
    pins are first crimped onto the prepared wire ends, and then the pins
    are inserted into the plastic connector blocks. There is a metal tab
    on the pin that locks it into the connector block once it is inserted
    far enough.

    It sometimes happens that, either because one wire is a tiny bit too
    short, or due to sloppy workmanship, one pin doesn't get "locked" into
    place. When the connectors are subsequently mated, the loose pin is
    pushed back in the block w/o making a secure connection. Normal
    vibration and/or temperature cycling can then result in an
    intermittent contact.

    FWIW, this can be a major PITA to find, but is easy to fix once you
    find it; just push the wire/pin in 'til it locks. The wrench at the
    dealership _should_ know this, and know how to deal with it. Again,
    I'd make it their problem.

    Hope this is helpful.

    ByeBye! S.

    Steve Jernigan KG0MB
    Laboratory Manager
    Microelectronics Research
    University of Colorado
    (719) 262-3101
    S, Nov 17, 2009
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    JD Guest

    You would need to have the ECU scanned. There may be pending codes that
    wouldn't light the MIL light. That is the code I am referring to.

    If they check the ignition modules, it may show up if the module is weak.
    Maybe not though. As I said; intermittent faults are hit an miss.
    JD, Nov 18, 2009
  8. Yeah if there is no meaningful code stored (I might discount some
    generic misfire code - dunno) I'd strongly suspect the ECU. Seems to
    me an intermittent from any sensor would throw a code pointing to a
    wiring or sensor issue. No repeatable/meaningful code - probably means
    the ECU itself is shutting things down. And I would have a serious
    discussion with the dealership and/or a regional Subaru Rep. I think
    I'd begin documenting everything too.
    1 Lucky Texan, Nov 18, 2009
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