F***ing computerized electrical crap - headlight switch

Discussion in 'GM Electrical Tech' started by pmf608, Sep 10, 2011.

  1. pmf608

    pmf608 Epic Member 5+ Years 1000 Posts

    Solved - F***ing computerized electrical crap - headlight switch / remote start

    Tonight I decided to install footwell courtesy lights in my Avalanche since the brackets are there and my (base model) silverado had them and the newer, loaded-out avalanche did not. The installation went well, and I powered them off of an unused factory lighting circuit - right down to adding a pin to a factory harness. All I had left to do was secure the grounds for the light sockets. I left the truck for a couple of minutes to get a wrench with the door open and interior lights on, including the new footwell lights - everything worked fine. When I got back to the truck, the lights were off. Thinking the computer had just timed them out again to save the battery, I tried opening and closing a door to reactivate them, but to no avail.

    At that point, I start to think that's a bit weird, so I try to start the truck. "Unknown Driver" appears in the DIC, and the truck shuts off as soon as it starts - as if Passlock is cutting power. My interior lights still don't work. Power door locks, windows, and right hand mirror don't work. seat memory doesn't work, but the power seats do. Radio doesn't work. Instrument cluster powers up but gauges don't work. Now I start to panic thinking my BCM somehow fried itself or died.

    So, I came inside to do some research on the internet, being very concerned at this point. Nothing useful that I could find online or in GM service info other than to check for shorts.

    Next step, go back out to the truck and check for any wires that might have shorted - I wiggle everything I touch and nothing changes. So I try the dimmer switch on the headlight switch and it doesnt work. Turn the switch from AUTO to the park light setting and the interior lights come on, windows and door locks work again, and the truck starts. Turn it back to auto with the truck running and the security light turns on. Then service 4WD, airbag, and ABS, and the DIC says "Unknown Driver". Switch it back to park lights, and everything works again but the security light stays on. When I turn the switch to park lights or on, everything works fine but if i don't have the interior lights overridden when I turn the switch back off after the truck is off, the interior lights will stay on but the other symptoms remain so my remote door locks wont work.

    So, now for the summary: My headlight switch seems to have fried itself and because it is tied to the computer like everything else in the truck, it is causing communication issues between the BCM and other systems, which causes no radio, no gauges, service messages, and door modules not to work. I wont be able to get a new switch around here until monday so until then i guess i will just have to lock and unlock with the key and drive everywhere with my park lights or headlights on:grrrrrr:

    I just hope that this post might be useful to someone else with a faulty headlight switch that causes strange symptoms. And who would have thought that a headlight switch could cause a no-start condition.

    Last edited: Sep 12, 2011
  2. Enkeiavalanche

    Enkeiavalanche Loving the Outdoors Staff Member 5+ Years ROTM Winner 5000 Posts

    I just don't understand it... I have added lights all over Both of my Avalanche's My old 02 and my 08. Never had a problem like that. People have added LED's and had some problems but most were simple to fix...Keep us updated.....
  3. pmf608

    pmf608 Epic Member 5+ Years 1000 Posts

    I don't get it either. You would think that it should be perfectly fine to add factory lights in factory locations on factory circuits - and it was. I also had all sorts of lights and wiring on my '01 Silverado that connected different lighting circuits in a variety of ways and never had any problems with the factory wiring. This is ridiculous considering I never even touched the headlight switch last night. Based on the fact that my truck still works perfectly with the park lights or headlights on, I'm hoping this will be dealt with when I get a replacement switch tomorrow.
  4. pmf608

    pmf608 Epic Member 5+ Years 1000 Posts


    I just got back from the auto wreckers where I bought, tried and returned a different headlight switch. The headlight switch didnt change anything. Sooo, this likely just became a GM dealer fix because apparently my BCM is broken and will only work if it senses the signal to turn the parking lights or headlights on from the switch - the automatic headlights dont have the same effect.

    This could be expensive now. So, here is my new plan:

    1) while I'm out trying to fix my Ford this afternoon (broken fuel pump on that one) I will try disconnecting the battery on the Avalanche for half an hour or so and see if it will maybe reset the BCM to work properly.
    2) Failing that, I will have to put up with this irritating crap until the Ford runs again because I cant be without a vehicle to get to school.
    3) If the avalanche doesn't sort itself out, I will have to take it to my local dealer for service. I've worked with the diagnostics guys there and they are top-notch, but thats at $139/ hour and the possibility of needing a whole new BCM.

    Bottom line is that this is ridiculous and if the disconnecting the battery doesn't reset the BCM and fix this, this could be an expense that I REALLY don't need.
    Last edited: Sep 12, 2011
  5. pmf608

    pmf608 Epic Member 5+ Years 1000 Posts

    Well, in one last-ditch effort to fix my truck before it went to the dealer, I decided to check all of my wiring under the dash one more time. This time I found a wire from my remote starter that had somehow been cut clean through. When I touched the 2 sides together, everything came back to life. I don't know how this remote start was wired in that it has become an essential and apparently non-removeable part of the truck, but reconnecting the 2 sides of the wire fixed the problem. It still seems strange to me though that turning the parking lights on seems to effectively activate the BCM in the same way.

    Now, if I could just find my soldering iron I would go and fix that little bugger.
  6. tbplus10

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

    How'd the remote wire get sliced?
  7. pmf608

    pmf608 Epic Member 5+ Years 1000 Posts

    It must have got caught on one of the wires I was running and sliced by some of the sharp metal brackets on the dashboard :neutral:

    Another question that comes to mind is why the remote starter was installed as such an integral part of the truck. I've never seen an aftermarket remote starter that was wired in a way that it was integrated rather than add-on and couldn't be disconnected. Based on this, it seems that however this one was installed would make it so that if the remote starter was ever removed, the truck would have the same problem I just had.
    Last edited: Sep 12, 2011
  8. Zzyzx

    Zzyzx Member

    If your truck has Pass-Lock, the remote start would have to bypass that somehow to in order to activate the fuel pump and such, so perhaps it is tied into that system.
  9. Rockstarrchevy81

    Rockstarrchevy81 Rockstar 3 Years ROTM Winner 1000 Posts

    Hey man this is CRAZY i just had the same thing happen to my truck a few weeks ago! I started my day off as i usually do and went to my College classes and truck was running fine no signs of anything and then when i get back in it after i parked it it would turn on and motor wouldn't even try to turn over or anything after i left school and was done for the day at home! I have the Seriveice 4 wheel drive light, Service air bag,Service tire monitor system and also my radio want turn on but everything else on the truck works as far as lighting! I also have a aftermarket Python remote start and security system and have been told by my buddy the BCM is prob throwed off due to the auto start and everything and might be a wiring issue with it! I took the alternator and starter off and got them checked they are fine and run like new and my battery went dead also got it replaced and left it unhooked since the other one it just drained!!!! Also on the dash it has the Gold Lock as if it's locked for Anti Theft and the truck want do anything. I was told either wiring could throw the whole bcm off and it want start and the auto start could somehow throw a code that want let the truck fucntion!

    I know for a fact the fuel pump is okay it primes you can hear it and the battery,alternator and starter are also fine. I checked my battery cables no corrosion on them at all and all Fuses are okay and not blown along with spark plugs are fine! I have checked everything i can and am pretty sure the ignition switch is fine also since there shouldn't be a problem with a truck with only 60k miles! I got the truck towed Friday For Free with USAA insurance thru the Military and will find out if it's the auto start monday since i told them to check the BCM and auto start for shorts and trouble codes!

    I think if problem is resolved when my buddy installs my Recon Smoked cab roof lights and installs my headlight, tail light, third brake light and turn signals on tow mirrors smoked tint film i will be gettin the Python Auto Start and Security system taken off and will be selling on Ebay since i paid almost $800 for this!
    Last edited: Sep 25, 2011
  10. sgtsjj

    sgtsjj Rockstar 3 Years 1000 Posts

    Im glad you got it sorted out to say the least, electrical crap does suck, its amazing how one wire can throw everything off

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