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Thread: reman/replacement PCM

  1. #1
    Potential Tuner
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    Oct 2019
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    reman/replacement PCM

    So I apologize if I havent searched the right key words, both within the forum and on google I know someone has already had to have asked this question.
    I have a 2000 Gm LM7 pcm from both a GMC Sierra and a 2000 Chevy Tahoe. My DD is the 00' Sierra but the 42? fan output and the recirc door output pin has decided to supply ground at all times with key off(battery voltage of 12.47v thru that pin and its bleeding roughly~6.7v on the recirc door pin(just enough to activate the relay for the low speed fans on the 3 relay circuit)on both the blue and red connectors) and sets my fans on full blast at random times, (to the point I went out into my driveway at 2am with a shotgun thinking someone was stealing my truck.) and that my battery obv was drawn down completely.

    so my question is: how do I copy/paste my sierra tune into my spare tahoe pcm that I have? ( I verified that pcm does not supply ground to the fan control pins for the fan output and the recirc door output, however obv with the vats/ different VIN it shut things down quick, which I expected, nbd.

    I guess the boiled down Question is: do I need to spend another $100 to license the "new" pcm or can I somehow just control C/V to make a computer copy of my current pcm with its vats/vin/current parameters onto my spare lm7 5.3 tahoe PCM? and if i need to spend the $100 it is what it is, but then, how do I go about it?
    I already fear that it isnt that simple but I just need my fans to work as commanded by the pcm, even for winter, georgia needs cooling fans in december and this is a work truck, I DD it and I tow/ lock into 4low regularly.

  2. #2
    Tuning Addict 5FDP's Avatar
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    If you knew someone with a GM dealership level tool, they could just flash the tahoe computer with your VIN/OS and it would make it another Sierra file. You'd have to license that computer after the fact if you wanted to change anything else.


    I believe another option would be to license that tahoe computer. Then use the compare feature within the editor, you could do a complete copy/paste of the sierra file over the tahoe computer to make it like it was before. Using the copy/paste or segment swap if they are the same operating system is a free thing to do so it would only cost you credits once for the tahoe computer.


    I do have one question though, both of those trucks would have come with clutch fans from the factory right? Electric fans for the radiator didn't start until 2003 for the silverado half tons. So are we talking PCM or BCM because the body control module HP Tuners can't do anything about that.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  3. #3
    Advanced Tuner
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    Bunch of HVAC/recirc junk in the PCM. Guessing e-fan(s) added, C1 #42 is the pin F body P01s use for Fan 1 control.
    Attached Images Attached Images

  4. #4
    Potential Tuner
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    Oct 2019
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    Yes you are both correct, they are clutch fans and I did add Efans and switched them on with the mpvi2 thru the pins blindsquirrel is mentioning. I did verify that by switching them off in the tune, they still come on, as well as when both the ecm1 and ecmB fuses are pulled from the fuse block, still on.

    I do have a buddy that works for a Cadillac dealer over in Alabama, I'll have to see if he may have access to that!

    Licensing the tahoe computer is probably what I'll be stuck with, it is also 4x4 with a 5.3LM7/4l60e so everything should come up matching fairly close.
    My only follow up question is how do I copy over the vin number? Im just not sure if the states emissions test pulls the vin from the pcm as well as when they scan it in to verify that they match.

  5. #5
    Advanced Tuner
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    Using the dealer (or equivalent) tools... If you plug in the Tahoe computer, and put the Sierra VIN into the GM software (TIS2000/TIS2WIN), the Tahoe computer will magically turn into a Sierra computer with the original Sierra VIN. From there you can copy back in the changes you've made to the current PCM.

  6. #6
    Senior Tuner Russ K's Avatar
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    Dec 2005
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    Just install the replacement PCM, then using 2 credits, do a write entire with your tuned Sierra .hpt file. And relink the VATS.


    Russ Kemp