Hoping not an ECU. Need Help Please

Discussion in 'GM Electrical Tech' started by Blazerado, Mar 29, 2013.

  1. Blazerado

    Blazerado Rockstar 100 Posts

    2004 Chevy Silverado 4.8. Sometimes it starts and sometimes it wont. I always have battery lights and all proper indicators. I have checked all cables and theyre good. I swapped the relays for the starter and the parking light. Lights worked fine but still not start. I even went as far as to jump the pins for the relay with no success. The starter is good and im all out of ideas. Any help is very appreciated.
  2. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Sorry, but I gotta ask the obvious, how do you know the starter is good?

    It has been my experience, that the usual reasons for a starter not to work, is:
    - foremost, the battery is worn out.
    - a battery cable is bad, or the connection is dirty.
    - the solenoid on the starter is worn out.
    - the starter is worn out.

    After that list is checked, the uncommon things are:
    -the starter relay,
    - a fuse.
    - the ignition key.
    - the wiring to the starter.

    One of the above is probably the problem.
  3. Blazerado

    Blazerado Rockstar 100 Posts

    Had starter tested and it checked out. That was my first thought even though the trusty hammer trick didn't work. Battery and cables are new. Starter relay works,fuses are good, tried both new and old key makes no difference and all wiring is ing good shape. Have power going to starter but ive heard the pcm gives the solenoid a ground signal to activate it. Not sure if that's correct or not.
  4. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts

    Your ecm has 3 wires to make the truck start, ground, 12v ignition, and most importantly 5 volt reference wire. The 5 volt reference wire is crucial, because It is first sent through the BCM then if the proper "resistance" is read, then it sends the signal to the pcm which in turn lets the starter engage. Hopefully your not having VATS issues, I wish you luck!
  5. Vinniety

    Vinniety New Member

    You are indicating it doesn't start but do you mean the starter doesn't engage. I think the thread is a little confusing. Anyway if you are referring to the starter not kicking over I would check the items RayVoy indicated which are the same things i would recommend but plus check if you have a alarm system. I use to install them years ago and sometimes we used replays to bypass certain items or add features and that can be an issue. Look under the dash and see what you see it will never hurt. I removed a stack of wires which i called a dish of linguine from a truck i bought because of similar random issues and after all the crap i removed everything eventually worked. Door locks, factory alarm, hazards. Its amazing what an aftermarket alarm can do. Good luck.

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