Frustrating charging system issue, 2000 GC

Discussion in 'General Motoring' started by jgmclean0, Feb 21, 2007.

  1. jgmclean0

    jgmclean0 Guest

    It's a 2000 Grand Caravan 3.3L, high mileage.

    The charging system seems to be failing intermittently but
    increasingly. Things will be fine for several days then I'll get a
    battery light (low voltage) and then the car will die as the voltage
    continues to drop.

    Replaced battery and checked the entire charging system (passed all
    tests with alternator putting out good voltage and amps) but ran into
    the same problem a week later when the new one discharged.

    During one of the "events", I measured 11.5V and dropping running at
    2K RPM (and only slightly less turned off); took this to be an
    indication of a bad alternator. Yesterday I took the alternator out
    (and what a job that is) and brought it to the parts store, where it
    passed their test with flying colors. Put that alternator back in,
    cleaned and tightened all battery connections etc. and immediately got
    14V into the battery. Hooray.

    Of course this morning I am back to the battery light being on and no
    apparent charging all day (less than 10V upon returning home).

    So, after a bit more research, I am left with these possible theories:

    1. Bad body control module -- the voltage regulator is apparently
    integrated into this computer (!) and if it is bad it could be
    preventing the charge from reaching the battery.

    2. From a glance at the Haynes book at the store there appears to be
    an "MDS relay" (I may be misremembering the name here) between the
    alternator and the battery; no relay by this name appears to be in the
    main relay center next to the battery and the relays under the dash
    are unlabeled. If anybody can tell me where to find this relay I can
    have it checked.

    3. Grounding problem, probably to the computer module. The ground
    connection to the battery is good; not sure how to proceed with
    checking this.

    4. Truly bad / intermittent alternator -- I've never heard of one go
    intermittent in this way; a replacement is a nonrefundable $180 and I
    hate to shotgun without knowing.

    5. Bad (brand new) battery -- don't think this can be it, since it
    takes and holds a charge from a battery charger, and runs the car for
    a reasonable amount of time before dying.

    Any other ideas, or ways to narrow this down. I am tearing my hair
    out here and the cost of sending an electrical gremlin to the shop is


    jgmclean0, Feb 21, 2007
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  2. jgmclean0

    Joe Guest

    If it stays off all day, it would be an absolute breeze to troubleshoot if
    you knew how it was supposed to be. Since it works sometimes, that should
    be easy too. Take some baseline voltage measurements when it is working.
    Take the same measurements when it's not working.

    Using that, it should be extremely easy to isolate the problem at the
    alternator. In other words, either the alternator is STOPPING or something
    else is TELLING IT to STOP. You just need to know what each wire on the
    alternator is for. If you have a shop manual, again, this should be no

    I wouldn't pull my hair at all until I'd figured out what component chose to
    shut down the alternator.
    Joe, Feb 21, 2007
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  3. jgmclean0

    sqdancerLynn Guest

    Not sure if it pertains to yours. Some of them the voltage reg is part of
    the body control computer So I would be checking the computer grounds
    sqdancerLynn, Feb 21, 2007
  4. jgmclean0

    damnnickname Guest

    First of all toss the Haynes manual in the trash can, its wortheless. The
    BCM does not in any way have control of the generator. When you say the
    voltage dropped down 11.5 5 did you measure this at the battery or the Gen
    Batt stud? this would make a big difference as to where the problem may be.
    If you checked it at the alt stud and it is indeed low I would then check
    for continuity between the generator field terminal DG wire to the PCM C1
    connector pin 8 for a tight fit or broken wire. you may even want to do a
    wiggle test on this. The other thing to be aware of is if you had an over
    charge or undercharge condition the Check engine lite should be on setting
    a fault code. I see no mention of you checking for any faults. Normally if
    no faults are set the generator is working and the problem would be from
    the Generator batt stud to the battery. MAKE SURE THE TERMINAL FOR THE
    GROUND AND B+ ON THE GENERATOR IS NOT BURNED. ALso take a good look at the
    40 cartridge fuse in the PDC. for a burned condition that may be causing
    intermittent contact. This happens alotwith alt. radiator fan and a/c
    compressor intermittent problems

    Glenn Beasley
    CHrysler Tech
    damnnickname, Feb 21, 2007
  5. jgmclean0

    damnnickname Guest

    oooops one more thing , the relay you are referring to is the ASD relay.
    make sure that when the engine is running you have 12 volts at the DG/OR
    wire at the generator connector also. If the generator is not
    charging...while the engine is running ground the generator field wire DG
    wire at the generator with a voltmeter at the battery to see if the output
    rises to 13 or more volts. if the output raises..... then you have an open
    circuit from the generator to the PCM. if that wire tests good replace the

    damnnickname, Feb 21, 2007
  6. jgmclean0

    jgmclean0 Guest

    Glenn, thanks very much for your response here.
    At the battery; not sure how to check it at the alternator.
    No check engine lights or fault codes, just the battery symbol light
    and corresponding voltage measurements at the batt.
    The main thing I am getting from this is that I won't get anywhere
    without a shop manual (or at least the relevant pages from one) since
    I have no idea where to find these test points. Any ideas how to
    proceed there?
    How is that one labeled? None of the fuse names on the inside cover
    of the PDC looked promising.

    jgmclean0, Feb 21, 2007
  7. jgmclean0

    jgmclean0 Guest

    Where do I find it?
    I think I actually understand this procedure, though again I guess I
    will need a shop manual to know which pins are which.

    As a point of interest, how do you actually do these measurements?
    The connection to the generator does not allow access to the pins even
    if they could be reached. Perhaps in the shop you have a special jig;
    how do I do it in the garage?

    jgmclean0, Feb 21, 2007
  8. jgmclean0

    maxpower Guest

    I gave you the color of wire that each one represents and the pin number
    that the wire goes into on the PCM. The PCM connectors are numbered
    I dont know why you need a shop manual, once again I gave you the color of
    each wire and pin number to the pcm and what the voltage should be
    If they arent labeled check at least check the ones that say 40amp. if you
    tap on them with your hand while the engine is running you may see a spark
    inside the cartridge if there is a problem with one
    maxpower, Feb 21, 2007
  9. jgmclean0

    maxpower Guest

    Ok, first of all you wont need to find it if you have 12 volts at the
    generator (Dark green with an Orange tracer wire)
    Once again, I gave you the color of the wire and the pin number that it goes
    into the PCM. No shop manual is needed ESPECIALLY a Haynes Manual
    With a DVOM meter
    I have no problem with this at the shop, no speacila tools or jigs needed
    maxpower, Feb 21, 2007
  10. jgmclean0

    jgmclean0 Guest

    Ah. I hadn't parsed DG/OR as a color code. In general I'd be more
    comfortable doing this with a diagram in hand, but I will give your
    procedure a try (probably a Saturday morning project at this point).
    I thought you were suggesting I measure the voltage at the alternator
    terminals as well as the input to the PCM, which led to my question as
    the contact points at the alternator are within a connector and
    difficult to access anyway.

    Thanks again

    jgmclean0, Feb 22, 2007
  11. jgmclean0

    Bill Guest

    Bill, Feb 24, 2007
  12. jgmclean0

    jgmclean0 Guest

    Just wanted to follow up on this, for the benefit of any future

    The problem did turn out to be the alternator. This is apparently a
    rare occurence (and in fact the alt had to be special ordered), but
    after 190K miles I guess it was time. The original alt had become
    intermittent based upon temperature and vibration, which explains why
    the first time I took it out it passed the test at the parts store. I
    had gotten it to the point where I could "activate" the alt after
    starting the car by tapping the bracket with a hammer; when this got
    tiring (heh) I bit the bullet and bought the new alternator.

    A couple of notes: this is really a tedious alternator to replace.
    You have to remove the wipers and the entire wiper assembly (including
    electrical, washer hose, and drain connections, and multiple bolts to
    release the alt from the bracket. The bracket itself is held to the
    engine by indeterminate means; I never could find the final bolt to
    remove the bracket and had to manhandle the bracket out of the way to
    get the alternator out (and had to remove the coil pack to do that).
    Dealing with the tensioner and belt routing on this car is always a
    challenge; be sure you have a belt routing diagram or make one before
    you remove the belt. Replacing the belt is easier if you remove the
    wheel and wheel well plastic from the right front. In short, it's
    well worth any effort to verify the status of the alternator before
    removing it to avoid having to do it more than once, and it's a
    stretch job for the DIY mechanic.

    The new alternator came with a nice tech note (TT #651 from Publitech
    Inc.) that concisely explained how to determine if a no-charge
    condition is actually due to an alternator problem, and included many
    of the caveats mentioned in this thread (a little late for me but
    there you go). I suspect that the parts store (in my case Advance)
    could pull this up for you without having to purchase an alternator.

    Belated thanks to all who helped here and via email.

    jgmclean0, Apr 4, 2007
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