1999 Chevy Lumina Security light

Try the relearn. If it doesnt take care of it, you may have to have the BCM scanned for codes

GM PASS LOCK RELEARN- Ignition to "run" position, try to start and let key return to "run" position
Approx ten minutes security light will go off
Turn key "off" and wait 5 seconds
Repeat 2 more times for a total of 3 relearns.
Turn key off, then start it

I have a 97 Lumina and the security light was on all the time but the car would start and run no problem. It turned out to be the sensors in the key cylinder, were not seeing the resistor chip on the key. I disconnected the 2 sensor wires at the bottom of the steering wheel and soldered in a matching resistor across the wires that continued into the dashboard. After a few minutes the security light went out and all is fine.
The wires were in an orange wrapping, both wires were white and went to a 2 position connector, the wires coming out of the other connector each had strips on them. I had to buy 2 resistors at radio shack that added up to my key resistance and solder them in across the connector. The connector going up to the steering wheel was left open and I just tucked it away. Now any key with or without a resistor will work as long as it is cut the same.