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.

Now it started and drove normally, unlike many searches on the Internet, which said theirs did not start.

Why would the SECURITY light just go on for a while then go off, and appearntly nothing happen with the car?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

The Security light in my 2000 Blazer came on twice while I was driving it to and from work the other day. Both times it happened about 3 miles into the drive. No effect on driveability. I shut down and restarted the engine and that kept the light off for the remainder of the drive.

I disconnected the battery and the light has not come back on the last two days. All the Owner’s Manual states, is that the Passlock system is disabled and to take it to a dealer.

Ed B.

I had the same problem with my 03 Impala when the door locks would not engage due to a blown fuse. The manuel is not really clear but when I replaced the fuse the light went out. Before I found the fuse, I would lock the doors manually and the security light went out as well. Do you have electric door locks? Do they work properly. Does the doors lock automatically when you shift into Reverse or Drive? I think it is tied to that system. The Security only means that there is something wrong with the door locking mechanisms I think.

My 03 Impala started blowing fuses on the door lock circuit and the security light would come on and engine not start, then the electric trunk release died. Finally replaced the Body Control Module (expensive) and everything resolved.