Electrical issues - believed to be theft deterrent related or ... ?

Discussion in 'GM Electrical Tech' started by Bowtie Junkman, Nov 3, 2011.

  1. We have a 2007 Silverado 1500 LS 2WD 5.3 (new body) that I bought used with 47K miles for my teenage son back in April.
    When we got it, it had an aftermarket alarm system already installed in it, so we did not get an original fob ... just the one supplied with the alarm.
    In addition to the alarm, someone has done a manual-to-power-window conversion, and installed an aftermarket stereo.

    I'm having a few electrical problems with it ...
    1) Sometimes at start-up, when turning the key to the "Run" position, it does not engage the starter. Dash lights, stereo, dome light ... everything works ... except it will not crank. Funny thing is, if you tilt the column down, or sometimes turn the key on and off 2-3-4 times, it will then start as normal.
    2) Sometimes when you start it, it will fire for a moment, and then die. It sometimes takes 5 to 15 starts to get it to idle on its own. And during this problem period, pressing on the gas pedal yields NO response from the engine at all ... just starts for a moment and dies.
    3) Sometimes, while driving, the theft deterrent light on the dash will illuminate. When the light is on, the turn-signals will not work, and neither will the hi-beams. The light will sometimes turn off by itself after a few minutes, other times will stay lit until you turn the truck off. But when you restart the truck, it will usually stay off.

    Notice I've used the word "sometimes" quite a bit ... that is because these problems occur sporadically. The only one that seems consistent is scenario #1 with the "no start" problem.

    Thinking scenario #2 was a mechanical problem, I've looked at engine wiring, mass-air-flow meter, etc ... but the more I read, the more I believe it might be related to the theft deterrent system (as the posts I've read about problems related to this system seem to sound very much like the one I am experiencing).

    We have since disconnected and removed the "brain box" for the aftermarket alarm ... but these problems still persist.

    In speaking with friends (car guys), we believe it may be possible that scenario #1 may be caused by a wire from the aftermarket alarm tapped into the exciter wire for the starter (ignition kill) that is causing a bad connection ... hence the problem "curing itself" when the column is tilted downward.

    But the theft deterrent light coming on and causing other electrical failures still baffles me. And the "start-then-die" scenario sounds like it also theft-deterrent related ...

    I want to go under the dash and remove all remnants of that aftermarket alarm, but not sure if that will cure the problem if it is related to the FACTORY theft system.

    Should I also consider it could be a problem with my key (it is a factory key with the + sign and black end) ... or should a get an original fob and a new key and try to see if that cures any of these problems?

    I am bound and determined to figure this thing out ... with a little help from my friends, of course.

    Thanks in advance ....
  2. zigger215

    zigger215 Member 2 Years 500 Posts

    Hello, I've been installing auto starts and security systems for over 8 years now and I have to say you are on the right path. I would remove the wiring from the security system and reconnect the cut starter wire. Your system is can-bus so really a starter kill install is not a wise idea but if the culprit had no clue what has was doing then he wouldn't know this. Uninstalling is a fairly simple task but I believe it would solve all of your problems, even the weird idling one. Chime in with more questions as they arise!
  3. pmf608

    pmf608 Epic Member 5+ Years 1000 Posts

    Based on your difficulty starting the truck, I would say possibly the ignition switch is bad since that can cause a lot of issues you wouldn't expect it to. BUT, since it has an aftermarket alarm, I would check to see if there are any wiring connections made in the steering column. This would explain the tendency to work better if you tilt the column down - there could be a bad connection that gets connected when things move.

    Speaking from experience, I would also just make sure there are no cut or shorted wires for the aftermarket alarm. I accidentally cut one of the wires for my remote starter a while back and because of the unusual way the installer had wired my remote start, it caused a major computer failure where none of the modules in the truck would communicate with eachother unless power was backfed by turning the park lights on. This meant my truck would be shut down by the theft deterrent, no gauges, no radio, no interior lights, no power windows, no power locks, no remote start, truck didnt know whether my key was for driver 1 or driver 2, etc. Once I found and reconnected the wire for the remote start, everything went back to working properly.
  4. zigger215

    zigger215 Member 2 Years 500 Posts

    sounds like the pass-code wire got cut....also known as pass-key + system, i hate that wire lol, why cant chevy be more like ford and use a simple transponder system???????...< wow did i just ask to be more like ford...thats blasphemy, sorry guys!
  5. sstoner911

    sstoner911 Epic Member 5+ Years 1000 Posts

    I would have that alarm removed completely of have a professional redo it. Sounds like it was installed by a novice.
  6. Thanks for everyone's advise. I plan on removing the knee-board and steering column covers tomorrow and removing all the wiring having to do with that aftermarket alarm ... and while doing it look for any suspicious connections.

    The funny thing is, we unplugged and removed the alarm "brain box" from under the dash weeks ago .... there is still a wire connected to the under-hood fuse box, but without the actual alarm "brain box" installed, I would have thought it would not have mattered. Oh well ... I guess I'll find what evil lurcks under my dash soon enough ... I'll be sure to post and keep everyone informed ...

    PS ... zigger215 ... I'd like to keep an eye open for that wire you referred to ... how can I ID it? Is the "pass-key + system" an electronic module under the dash somewhere .... or should a be looking for a specific wire/bundle of wires .... ????

    Thanks again to all for sharing your knowledge / experience / expertise ...
  7. zigger215

    zigger215 Member 2 Years 500 Posts

    PK+ system is GM's fairly complex security and anti theft system in the vehicle, in that particular truck you will see a harness going up to the ignition, the wires are much smaller then the old school ignition wire, this is because the electrical system in that truck is much more efficient. this harness will only contain five wires (this may differ depending on the trim level of your son's truck) these are your "ignition" wires, i say that with quotes because they are can-bus (GM data) so they are actually doing more then just your ignition functions. This could be why your son's truck is acting so strange. If one of these wires is cut or broken it will cause erradic behavior in your truck. The wire they may have cut is a + starter wire, it is purple and will be located at the starter or fuse block under the hood. The second starter is a little more tricky this one will be in the little ignition harness and is actually composed to two wires The first wire is either pink/black or pink (depending the month your truck was manufactured) and the second wire is white. make sure thesee wires are seperate from each other and run continuously all the way to the ignition, these are data wires so they are handling more then just start up. Your ignition wire is pink and your acc. wire is either brown or yellow depending on the month. There is a power wire in the harness but its current carrying capacity isnt great enough to handle the draw a security system requires to operate, hopefully they didnt tap into this wire, if they did simply disconnet their wire and make sure this wire runs continous. I hope this didnt confuse you, i sometimes ramble.
  8. A lot of info to ingest .... but all excellent none-the-less ...

    I'm assuming that the "rag-tag" alarm install would have used the type of connector that just "taps" into the existing wire with a "T" connection (sorry, I don't know the correct technical name for these type of connectors) .... if this is the case, is it safe for me to assume that I can remove this connection from the original GM wire/harness, check to see that the wire itself was not damaged in the process, tape it up and it should be good to go?

    The reason I ask is because you referred to the need for some wiring to be "continuous" ....
  9. pmf608

    pmf608 Epic Member 5+ Years 1000 Posts

    correct - if there is anything using a tap-connector like that, you can remove the connector and tape the factory wire up if it is in good shape. If the wire is broken, I strongly suggest soldering the 2 sides back together and putting heat shrinkable tubing on it. This is the right way to fix it and make sure you won't have future problems. This is what zigger means by continuous - just make sure the wires aren't broke or worn out or something like that.
  10. Cool .... looks like I have my work cut out for me ...

    Light a candle and cross your fingers ...

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