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Thread: Start circuit on E67

  1. #1
    Potential Tuner Glenn's Avatar
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    Question Start circuit on E67

    Hello,
    I am a newbie to tuning (via computer any way). I have an 07 Trail Blazer LS2and full vehicle harness in a 57 T-Bird. The Trail Blazer had an Automatic trans but the Bird has a TKO500. I have the GM service manual set for the 07 Trail blazer and have been tracing wires for a while. I have all the ignition circuits working except for the start circuit. I have traced power down the Yellow (circuit 5) into the fuse block, which turns to a purple wire (circuit 806) all the way to connector c1 - pin 1 on the E67 ECM. When I power this wire, nothing happens. Neutral Safety is hooked up and working per the schematics.

    In another part of the book it shows the PNP circuit going into the ECM through connector c1 - pin 56. This shows a circuit in the ECM (starter enable relay control) that grounds the starter relay in the fuse block. I swapped that wire in the fuse block for a direct geound and the starter energises whenever the ignition is on. this tells me that the Starter Enable Relay Control (SERC) is not grounding.

    What is the logic to trigger the SERC?

    Please help!

  2. #2
    Advanced Tuner Montecarlodrag's Avatar
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    I don't have the diagram for the SS trailblazer, but I have this for the 5.3L, it should be the same.

    Find the Park/Neutral switch signal on the PCM (dark green, pin 47) and hook fused +12V from the ignition switch (if you don't have a park/neutral switch on the car). It will enable the starter circuit on the PCM.
    Also, make sure the starter relay has +12V when Key is ON.
    When you turn the ingition switch to crank position, the PCM will ground the yellow/black wire and the car will crank.

    If the park neutral signal is not present the PCM won't enable the starting circuit, because it thinks the car is in gear.

  3. #3
    Potential Tuner Glenn's Avatar
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    Start circuit on E67

    Thank you, but all of what you mentioned (except the cranking part) is as you described.

    There is power to pin 47 of connector C3 (through a switch on the trans), there is power to pin 1 on connector C1.
    Since the TCM is gone, could the ECM be looking for a clutch release switch? I disabled that in the ECM, but what pins would take care of that?


  4. #4
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    The should be a Starter Diagnostic "master enable/disable switch" in the "System" tab of your software. Switching that off may negate the need for some of what you are trying to do.
    Jaime

  5. #5
    Potential Tuner Glenn's Avatar
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    Start circuit on E67

    Thank you for your help, but the issue was that the VATS was on and I couldn't see it since I had my EDIT/VIEW set to BASIC. I set that to Advanced, disabled the VATS and it started the way it should. The proce of just learning the software.

    The thing that made me think it was the VATS was that I replaced the wire in the fuse block that grounds the starter relay, and got it started. It would only run for 3 seconds, I read that VATS does that. I didn't see any place that VATS kills the starter.

    Thank you again,

    Glenn