300M Check Engine Light

Discussion in 'Chrysler 300' started by Percival P. Cassidy, Apr 5, 2010.

  1. Over the years the Check Engine Light on our '02 300M has activated, and
    the "key dance" has indicated that the fault code is P0440 or P0441.
    I've deactivated the light by disconnecting the battery or pulling the
    appropriate fuses, and the CEL has usually stayed dark for a long time.
    It's never re-illuminated in time for a regular service so they can
    check it out.

    Not long ago the CEL illuminated again, and I hadn't got around to
    either doing the key dance or pulling the fuses. But then when I drove
    the car on Friday I noticed that the CEL was not on. I mentioned it to
    my wife, who said, "Oh yes. All the instrument panel lights flashed off
    and on, and then when they came on again the CEL was off."

    What could have happened here? Spontaneous reboot of the computer?

    Percival P. Cassidy, Apr 5, 2010
  2. Percival P. Cassidy

    Bill Putney Guest

    Perce -

    My best guess is that something sucked the system voltage below the PCM
    reset level momentarily. One likely cause is that the battery has an
    intermittent internal short (that's often how they act towards end of
    life). Other possibilities are a momentary main bus short (to ground)
    elsewhere, or a poor (intermittent) connection either on the power
    system or ground.

    For poor connections, check: (1) Pos. and neg. right at battery (tends
    to be a lot of corrosion unless checked and cleaned periodically on
    these cars due to hidden battery location), (2) Positive jump post
    connections (*not* the battery post - the place where you would jump the
    car off - nect to the air cleaner) - *all* power (with the exception of
    the connection between the battery and alternator) go thru that junction
    and rely on good clamping, and (3) Negative jump post - located on the
    passenger side strut tower - that is the main vehicle ground point.

    How old is the battery?

    On the two codes you're getting - you do know that one of the more
    frequent causes of that are gas cap not being screwed on tight enough to
    seal, or defective gas cap. The fact that those codes are few and far
    between for you give hope to that. If that's not it, there is a valve
    and a couple of hoses that are the other common causes of that in the
    2nd gen. LH cars.
    Bill Putney, Apr 5, 2010
  3. New battery last November.

    And removing power by disconnecting the battery or pulling the fuses for
    just a few seconds doesn't usually reset the computer, does it? I've
    read that one should wait 10 minutes or so.
    I'd read that, and I replaced the gas cap. CEL still illuminates from
    time to time.

    It did switch off on its own at least once before -- without anyone
    noticing flashing instrument panel lights.

    Percival P. Cassidy, Apr 6, 2010
  4. Percival P. Cassidy

    Bill Putney Guest

    You are correct - *however*, that is without shorting the bus to ground
    - IOW, capacitors in the front ends of the various modules have to
    discharge by leakage currents for the bus voltage to drop to the PCM's
    reset levels - that's the reason for the 10 to 15 minute wait period.

    Experts know that *IF* you were to disconnect the battery and short the
    bus to ground (it would be better to use a resistor to limit current),
    the reset of the PCM occurs right away (only as long as it takes to
    discharge the total capacitance hanging on the bus) - which would also
    happen if the battery were to internally short, bringing the power bus
    momentarily to ground. ;)
    Then you likely have a problem in that valve or a break/crack in one of
    the purge system hoses (IIRC, one of the hoses is just under the air
    filter box) - details are available on some of the LH car forums
    (www.dodgeintrepid.net and www.lhforums.net). I've never had this
    problem on either of my Concordes, so I tend not to remember the exact
    Yes - some of these codes/CEL's automatically disappear after some fixed
    number (50 I think?) warm-up/cool-down cycles without the fault recurring.
    Bill Putney, Apr 6, 2010
  5. The CEL came on again, and I had pulled the fuses a few days ago. The
    CEL was still off.

    Earlier this evening -- still daylight, so the lights were not on -- I
    had to wait for a train, so I switched off the motor. After a minute or
    so I heard a rapid clicking noise from the left-hand end of the dash,
    and when I turned the key the instrument panel lights were dimmer than
    they had been, but I was able to readjust them back to normal brightness.

    I think I must have a bad (intermittent) relay -- or a bad connection to
    one of the relays. Finding which one could be a problem.

    Percival P. Cassidy, Apr 14, 2010
  6. Percival P. Cassidy

    Bill Putney Guest

    What year is your M? You need an FSM so you can study the schematics to
    figure which relays, etc., relate to your symptoms. I can email you a
    link to access an FSM for some years (and certain years are so similar
    that you're probably covered by an adjacent year).
    Bill Putney, Apr 14, 2010
  7. It's an '02, and I do have the service manual -- which I have not yet
    consulted. But there is a layout guide on the inside of the cover on the
    end of the dash, but no relays seem to have anything to do with the
    instrument panel -- fuses, yes, but no relays. I pulled and reinstalled
    the fuses, but I don't know whether that will accomplish anything.

    Percival P. Cassidy, Apr 15, 2010
  8. Hi!
    I hear that and immediately think "bad ground". Or a flakey ground
    connection somewhere. Bad or flakey grounds will cause all manner of screwy

    It's worth a look...

    William R. Walsh, Apr 16, 2010
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