Midwest Classic Insurance

Visit our community sponsor

Thanks Thanks:  0
Likes Likes:  1
Results 1 to 5 of 5

Thread: Main Rely wiring problem has me stumped

  1. #1
    Senior Member
    Join Date
    Dec 2015
    Location
    Huntsville, AL
    Posts
    103
    Post Thanks / Like

    Main Rely wiring problem has me stumped

    I'm in the process of rebuilding and rewiring my 818 after a fire.

    I'm using an 05 Legacy GT harness that I have dieted and working through all of the electrical problems. I am down to the last one (that I am aware of) and having trouble figuring it out, and it has to do with the Main Relay. A partial wiring diagram is below.

    When I turn the key to ignition, the main relay activates as it should, but when I turn the key off, the relay remains on (power to all circuits). I have to disconnect the battery to get the relay to reset.

    Main Relay.JPG

    Looking at the diagram, I assume the Lg wire connected to the ECM at location D16 is what activates and deactivates the relay. So, something in the ECM is controlling the relay and I don't have any information on what goes on inside the ECM.

    The only modification I made to this circuit was to splice the WG wire that goes to the front O2 sensor to also power an AEM wideband O2 sensor, and the controller/gauge. I tried unplugging the controller and still had the same problem.

    If anyone has any ideas as to what to look at for troubleshooting this, I would certainly appreciate it. All of the wires are pretty straightforward, but I'm not sure what is going on inside the ECM, or what dieting may have caused this problem.

    Thanks

    Skip
    Last edited by lclevert; 02-03-2019 at 09:07 PM.

  2. #2

    Yes, I love Technology
    aquillen's Avatar
    Join Date
    Feb 2016
    Location
    NW Indiana
    Posts
    752
    Post Thanks / Like
    The ECM does a "keep alive" on that relay. In my 2002 ECM for the 3.0 engine, it is about 30 seconds. It may be longer in newer cars, I believe one of previous corvettes I had for example was 3 minutes.

    So when the ignition is shut off, the ECM keeps the relay on for a while then turns it off.

    Check that the 12V ignition to the ECM, (same as goes to fuel pump), at ECM's B137 pin 15 (D15), does get turned off with the key switch.

    There is likely other things to investigate but that's the first place I'd go, based on what you wrote.
    Last edited by aquillen; 02-03-2019 at 10:34 PM.

  3. Likes turbomacncheese liked this post
  4. #3
    Senior Member
    Join Date
    Dec 2015
    Location
    Huntsville, AL
    Posts
    103
    Post Thanks / Like
    Ok thanks. Hopefully it is that easy. I never waited that long. I thought it was a problem and cut the power. I’ll look at it tomorrow and see if it eventually goes off.

    Skip

  5. #4
    Senior Member
    Join Date
    Dec 2015
    Location
    Huntsville, AL
    Posts
    103
    Post Thanks / Like
    I went out and tried it this morning and sure enough it reset after a little while. I would have never even known this was happening if I hadn't wired my wideband O2 into the same line as the front O2 sensor. I guess I just wasn't patient enough. You learn something new every day.

    Thanks for the quick reply Art.

    Skip

  6. #5

    Yes, I love Technology
    aquillen's Avatar
    Join Date
    Feb 2016
    Location
    NW Indiana
    Posts
    752
    Post Thanks / Like
    Why? So the ECM can watch engine temp and kick on the fans if needed (my best guess).

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

FFMetal

Visit our community sponsor