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Instrument cluster odometer question

Discussion in 'Minivans · Pacifica' started by Varkguy, Feb 6, 2015.

  1. Varkguy

    Varkguy Active Member

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    There's a little dispute going on on another forum about the source of mileage data for the cluster odometer reading on an 05 Caravan. For years I've been thinking mileage data is stored in the BCM and if you change the cluster the odometer will read whatever the BCM tells it to. No reprogramming required. Is this in fact the case?

    To expand a tad, the BCM went away on the 5th gen vans. Is the TIPM now the mileage source and would a cluster change on a 5th gen van still be plug and play so to speak?

    One more thing. How do you send a private message on this forum? I'm lost.
     
  2. Rick Anderson

    Rick Anderson Well-Known Member

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    I think, but do NOT know for sure, the mileage is stored in the PCM. PCM's tracked mileage before the digital odometers, and part of the PCM replacement is too use the Dealer Tool to write the VIN# and Mileage into the new PCM. The PCM uses the mileage as a factor to make adjustments to the engine tune. Later vehicles with anti-theft immobilizers do a check of VIN#'s from the PCM and BCM and other modules, if they don't match it won't let the engine start (I guess so you can't steal a car by swapping out the PCM).

    I have swapped PCM's on non-antitheft/immobilizer vehicles that also had a mechanical odometer, never wrote the VIN#/Mileage to the PCM and the vehicle ran just fine. I wasn't going to pay the dealer the hefty fee for 5 minutes of work to just hook up their special tool to write 2 number in the PCM.

    Obviously, if you have the anti-theft/immobilizer this will NOT work and the vehicle won't start until the correct VIN# is written into its memory. I suspect, but do NOT know for sure, if swap the PCM in a digital odometer vehicle, the odometer will read the mileage that is stored in the PCM.
     
  3. Rick Anderson

    Rick Anderson Well-Known Member

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    I think a better way to state above. I know for a fact the PCM tracks the mileage of the vehicle, that is uses that mileage as a factor for making adjustments to the engine tune. I don't know for a fact if the mileage tracked in the PCM is used for Odometer display or some other module tracks it. My suspicion is that the PCM is the source, its perfect for doing it, why would you waste money to build the same feature into another module?

    If I'm wrong, my first guess would be the instrument cluster itself, since the turn of the century most vehicles have instrument cluster be a microprocessor controlled module in itself as well. So for liability sake, they may have made the mileage tracked there to prevent someone rolling back mileage on a vehicle during resale with a junkyard PCM swap.
     
  4. valiant67

    valiant67 ...

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    That is what I understand as well - the instrument cluster is now a computer node.
     
  5. ImperialCrown

    ImperialCrown Moderator
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    The PCM tracks mileage, but only for its own purposes.
    The BCM tracks and stores mileage used for the instrument cluster (MIC- mechanical instrument cluster).
    The CCN (cabin compartment node) is the new instrument cluster that also performs many of the previous BCM functions. It now stores both the mileage and VIN. If you order a new CCN, the parts guy needs to know the current vehicle mileage. That will be the mileage that the replacement CCN will start from.
    The TIPM does not store the mileage. It is also called a 'Gateway' module and stores the options (sales codes) of the VIN it is assigned to. All modules may store the assigned VIN now. The scan tool may or may not be able to overwrite the VIN to a new VIN in some modules. There is a 'VIN mismatch' fault code.
    Swapping modules between vehicles nowadays is very risky (even for brief diagnostic purposes) as a new 'learned' identity after the secret-module-handshake over the communications bus can't be unlearned. The service manual says 'not to swap'.
     
  6. Varkguy

    Varkguy Active Member

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    Thanks to all for taking the time to answer. Ever wish you had a time machine that would take you back to the days when you could fix anything on a car in your backyard? I sure do.
     
  7. valiant67

    valiant67 ...

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    No not really because I remember the days of yearly tuneups - points, plugs, cap, rotor, wires, etc. and then hoping the points don't go bad while you are driving within that year. Then every 3 years or so rebuilding the carburetor. And radiator hoses that were lucky to make 5 years.
    Honestly it may be more expensive to maintain or fix things when it is necessary, but there's a whole lot less maintenance and repairs necessary on the vehicles I've driven now compared to back then. I like that. I can recall around 100k knowing that soon the starter, alternator and water pump were all going to need replacement probably in the next 10-15k miles. Now, I think nothing of the original 15 year old, 150k mile stater, water pump and alternator on my Dakota (and over 200k on the Dakota before). And I have to admit even the lower radiator hose and the heater hoses are still original.
     
  8. thedriver

    thedriver Active Member

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    well, what year? I replaced the base cluster in my 06 T and C with a tach cluster from an 05 Caravan with no problems, it just showed the correct mileage as if it was always there.
     
  9. John Wood

    John Wood Allpar Legacy

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    Per IC's post, the odometer mileage was in the BCM and that was what was displayed on your replacement cluster. I doubt you could get buy with such a swap on later model year vehicles.
     
  10. valiant67

    valiant67 ...

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    It's likely the vans did not switch from a traditional cluster to the new CCN style until the redo in 2008. I'm not sure the minvans were on the new CANbus until then.
     
  11. Varkguy

    Varkguy Active Member

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    05 as stated in the first line of the first post.
     

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