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Thread: The Zombie Undead DTC P1638 Code - Can't Kill It

  1. #1
    Fuel Injected!
    Join Date
    Nov 2019
    Location
    Bossier City, Louisiana
    Age
    65
    Posts
    339

    The Zombie Undead DTC P1638 Code - Can't Kill It

    Hello,

    I've read the one DTC P1638 thread discussion around here but overall, it was unhelpful. Tuner Pro RT won't let me kill the DTC P1638 code for "F" terminal control of the alternator. Tuner Pro can see these in the parameter tree view of any BIN that I look at. I can set it for nothing to happen and Tuner Pro will give me the asterisk indicating that I need to save the new setting. I then save the BIN.

    But if I reopen the BIN, my changes with regard to DTC P1638 have not been saved. I've tried different PCM's with different BINS in the vehicle and they all still see a P1638 fault. I've tried different alternators and still get the fault - can two alternators have the same fault? Unlikely, but I suppose it could happen. I think I will stop by a local alternator rebuild shop and see what they say about F terminal problems.

    I don't get a check engine light, just this annoying code that my scanner sees. My alternator appears to work well - 14.4 volts DC at idle without my fans running. With the fans running, its about 13.7 volts DC. And I only see a tiny amount of 0.012 volts AC at the battery with the engine running - the rectifier is ok.

    Any ideas why Tuner Pro won't let me kill this DTC?

    Many thanks,

    Rick
    1970 Chevy El Camino, LM7 Engine, 4L60E - Two 896 and two 0411 PCM's

  2. #2
    Carb and Points!
    Join Date
    Nov 2021
    Posts
    3
    i have been learning on the fly myself but i do know that in tunerpro if you open up the system then open up the table up in the top right hand side in the execute box put a "0" without the quotes then go to your system ( mine was gmt800 i followed that column down to the F terminal and double clicked in that box then i hit execute then save that should turn that off for you.

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