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Thread: Battery Draw Issues standalone E38 ECU . ECU won't go to sleep, Power Mode

  1. #1
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    Battery Draw Issues standalone E38 ECU . ECU won't go to sleep, Power Mode

    We are running full stand alone with a E38 controller and 6l80E no BCM. No issues other than the battery will go dead after several days.
    I have traced this down the the GM E38 ECU is staying awake all the time. If you plug a scanner in it will continue to read live data for days even after the key has been turned off. If you press that gas the pedal will read on the scanner coolant temp etc.... still live. Swapped different ECU's with same results

    I have verified my battery and switched voltages.
    X1-19 is switched 12volts
    X1-20 is battery hot all the time
    X1-47 is switched 12volts coming from the powertrain relay.

    I can actually unplug X2 connector and loose some data that comes in on that plug but the ECU still stay awake and sending TPS data etc.... so i know its nothing on X2

    The only other voltage on X1 is pin 61 EVAP VENT. I can unplug the vent valve and still have a issue so I know thats not it.

    Im thinking the ECU is either staying awake to run some sort of emissions test or is waiting for a signal from the BCM to power down.

    If its a BCM message that is is waiting for then why doesn't everybody with a E38 standalone have this issue, I have searched online everywhere and not one mention.

    If its an emissions test that it want to run is there a way to disable it or change the timers so the ECU will power down?

    If i remove the battery power from the ECU and plug it back in it will stay asleep until I cycle the key and then it will stay awake until the battery is dead.

    Anybody have any insight?

  2. #2
    Tuner in Training
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    Completely digging up an old thread here, but was this ever figured out? I have the exact same issue on my stand alone e38/6l90 swap.

  3. #3
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    X1 pin 19 is labeled in the factory diagrams as 'Data Communications' from the BCM, but that is actually a plain old switched 12v wire. Hot with IGN on.

  4. #4
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    Quote Originally Posted by blindsquirrel View Post
    X1 pin 19 is labeled in the factory diagrams as 'Data Communications' from the BCM, but that is actually a plain old switched 12v wire. Hot with IGN on.
    Okay, so how does that play into getting the ecm to go to sleep?

  5. #5
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    I don't know. If you really need an answer I guess you can try to contact a GM engineer. Personally I would connect all the IGN/BAT wires shown in the diagrams and see what happens.

    That switched wire also goes to the TCM, if used. I don't recall if this diagram is T42 or T43. Look up diagrams for what you have and wire it accordingly. Don't let the 'Data Communications' label throw you off.
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  6. #6
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    Maybe if there's no activity on that pin the modules default to ON, so that if that input is lost it won't die while driving? Dunno. Plausible though. Kind of like expecting RAP to function when you don't have door switches hooked up.

    Apologies if the notification email included part of my earlier message now deleted... I need to remind myself to read things closer.

  7. #7
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    Hmm. Okay that makes sense. I?ll dig in a little more on the diagrams and see what I find vs what I have hooked up. It?s been a while so some of these things aren?t fresh in my mind anymore. I?m using a factory wiring harness for the eng and trans though.

  8. #8
    I can't say this about a e38, but I did just about pull my hair out on a P59 that did that. I never could narrow down why, but I swapped out the ecm, and the problem went away, so it was the ecm.