07 Tahoe headlight/alternator issue

Discussion in 'GM Electrical Tech' started by TonyO51165, Mar 19, 2017.

  1. TonyO51165

    TonyO51165 New Member

    In need of some help please....I have an '07 Tahoe with headlight issues. Bare with me as I try and explain this the best I can....When I start the truck the headlights don 't come on when the switch is on auto. When I turn the switch to on, they still don't always come on. I have to turn the switch on/off several times, or barely turn the switch and they will finally come on. I thought it was the switch, changed it, but still the same. I've also just noticed that if I turn the lights off, the alternator won't charge. However, if I leave the switch on auto or have the lights on, the alternator charges just fine. I'm thinking a possible ground problem somewhere? I've checked fuses and they are ok...not sure how to check relays. Another thing I have noticed is, when I'm sitting in the truck without it being on or even having the key in the ignition, every once in a while I hear a click sound coming from around the door lock buttons on the arm rests. If I'm missing any pertinent information that might help, please ask and I'll try to describe or explain what ever I might be missing. Thank you in advance, I hope I'm able to get some help on this.........
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Have you hooked a diagnostic tool up yet and checked for any fault codes?
    Something many owners of newer vehicles are not aware of is the fact that these newer vehicles will give codes for issues but not give a CEL making you aware of a problem.
    Unfortunately your headlights, by route of an extensive wireing system connect to the BCM, Body Control Module, and then go out to the individual lights. Not saying it's the problem, just saying it's another item to check.
  3. TonyO51165

    TonyO51165 New Member

    No I haven't, I wasn't aware that it would give me anything. When I get to work tomorrow I will have our mech. hook his up and see if he can get anything. Thanks for the advice, I'll keep you posted.
  4. TonyO51165

    TonyO51165 New Member

    Ok, sorry for the long delay, I've had a ton of stuff going on and just haven't been able to get back on. I've done a diagnostic check on the system. It kicked a ton of errors leading to the BCM....I've changed the BCM, chgd the dash sensor and chgd the headlight dash switch. The only thing that started working was the day time running lights. But did not fix the charging issue or the auto headlights issue. I know it may be hard to understand, I have tried to explain the best I can....I may just have to do a video on it showing what it is exactly doing....This thing is an electrical nightmare.....any suggestions as to what to possibly look for next? Thanks in advance....
  5. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Let's look at it one item at a time.
    I don't think you have a charging problem. If I read your original post correctly, that is the way the '07 charging system works. GM has a techy name for it, I just call it smart charging.

    The PCM monitors the condition of the battery, the electrical draw and adjusts the output of the alternator to keep the battery charged at 80%
    So, when the lights are turned off, little draw, the PCM turns off the charging system; get headlights on, up goes the draw and on comes the charging system.

    Ok, the headlight problem..........maybe it's a power problem.
    These trucks ('07 to '13) have problems with the underhood fuse panel. I know a number of people who have had to have the fuse panel changed. The terminals, the wire connectors, the fuse baskets corrode.

    Tomorrow, ask your GM parts guy if he has a fuse panel in stock..................if they are stocking something like that, it is a sure sign that it is a frequently changed part.
  6. silverado002

    silverado002 Rockstar 3 Years 1000 Posts

    My best guess is (since you changed out the BCM) a possible faulty ground to the headlight switch. That ground goes to multiple places including the ambient light sensor and flash to pass turn signal switch. I'm not sure where in the cab the ground point is.
    Last edited: Jun 14, 2017
  7. TonyO51165

    TonyO51165 New Member

    Thx for the reply Ray....as far as the charging goes...I notice when I start the truck, the needle is above 14, then it starts to go down well below the 14 and that's where it stays until I turn the headlight switch on, then it will go back up to around 14...is that what you are speaking of? silverado002, I had heard something about a ground under the dash somewhere that may cause such problems....I have no idea as to where to begin looking though....what really stinks is, I bought this used from a dealer, of course it was daytime and didn't even thing to ck something like this...if I had known this had such an issue, I would've passed on it.
  8. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Tony, my '09 acts the same way. It does have a strange little cold morning feature, it will wait 10 to 15 secs before it starts to charge on a cold winter morning, acts just like yours in the summer time.

    The fuse panel gets wet from tire spray and it is a know problem...
  9. TonyO51165

    TonyO51165 New Member

    I'm in Florida....the cold does make it past the Ga. state line...hahha....I'll have to look in to the fuse panel issue....I'll keep you posted.
    RayVoy likes this.

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