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2003 Chevy Impala Security Light Question

On my 2003 Impala, I just had inspected and had a catalytic converter replaced on, for some reason had the SECURITY light on while driving for a little while.
<br/> Now it started and drove normally, unlike many searches on the Internet, which said theirs did not start.
<br/> Why would the SECURITY light just go on for a while then go off, and appearntly nothing happen with the car?


  • edited March 2009
    I wish I could give you a answer. I worked with these system a lot at GM. What I can confirm is you are not the only one to have a illuminated security light and nothing happening with the car.

    You could be on the other side of the coin with these systems, a car that won't crank with no apparent activation of the security stytem.

    The Factory Service Manual gives a good overview of the system complete with Body Control Module re-programing steps but it hasn't helped me solve the two conditions I have described.

    You are not alone with this mystery light. Like I said it can get worse,with the car not cranking,we have many posts on this Forum with this problem with Passlock 2 systems. My only answer is that I still don't understand the sysyem sufficiently.
  • edited March 2009
    If that light is on there should be a diagnostic code stored. Has anyone hooked up scanner to read the codes? If not then that's where you need to start.
  • edited March 2009
    Thank you for telling me that, because I have to take the car anyway today, so today would be a perfect time to have it looked at with a scanner.
  • edited March 2009
    I went to Advanced Auto Parts and after a scan, it said pass and No Error Code.

    So I don't know what the heck is going on, the light never came back on though.
  • edited March 2009
    The simple scanner used by the auto stores won't pick up codes for anything like the security system. You would have to get the code(s) read by a GM dealer or an independent that had invested in a good code scanner that can read the non-generic manufacturer codes.
  • edited March 2009
    Darn, I guess I will have to get it to a GM dealer then, but that probably will not be for a couple days.

    The car should be ok to run right? Until then, I mean.
  • edited March 2009
    My understanding of when the light is on it indicates "activated"or "armed" not that a failure has been detected.

    With the Ford PATS system your "THEFT" light will blink rapidly with key in "ignition" position when a fault is detected. There must be a illumination condition with the GM system that simply means "activated" and not indicating a fault.
  • edited March 2009
    Well, how does one activate or deactivate or is it automatic? I mean what is the SECURITY system.

    Yes, I read the manual, but it's not making any sense when I read it or when a friend of mine reads it.
  • edited March 2009
    This security system reads a code generated by turning the key (as I understand it) and the only security feature is disabling the starter when the wrong code is read.

    What I can't remember is how a different code is generated by each turn of the key.

    When you turn the key it tells the BCM what code to expect from the next turn of the key.

    Some systems use a transmitter in the key and a reciever antenna ring around the ignition switch (BMW and FORD) But GM's is slightly different

    In any case the system is passive with no input from the driver to arm,it does not sound a horn,blink lights,just disables the starter.
  • edited March 2009
    Lots on the Web about Passlock 2. If the light comes on while driving your car is not protected by the Passlock system.

    There is a Passlock module imbeded in the ignition lock cylinder. When you turn the key a signal is generated by the Hall effect system. A imbeded resistor sends or the BCM reads a signal and the signal must match a stored code or the starter is disabled.

    There is also a lot of info how to bypass a malfunctioning system.

    Earlier GM systems had this resistor embeded in the key.

    Many Passlock 2 failures are from the passlock module (need to replace ignition lock cylinder) and from moisture in connections.

    I wish I had a FSM to review this stuff
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