The security, antitheft or lock picture/icon is a visual indication that something in the car's antitheft system is failing. In most GM cars and trucks there is a hidden system that most people are unaware even exists. From the moment you put your key in the ignition, there begins a constant line of communication between your key's security chip or transponder, to the ignition's lock cylinder, and then to the car's TDM (Theft Deterrent Module). These 3 parts are in CONSTANT communication. If the key is in the ignition, then these parts are sending signals to each other. The security light illuminates when that signal gets broken, even just for a second. When the signal breaks, the car misinterprets this as an attempt at theft and goes into antitheft mode. The car thinks its being stolen or hotwired because it is not getting that signal from YOUR specific key. This is why the security light turns on and shuts down your vehicle. This link explains it pretty well.
Perform the re-learning procedure
- Turn ON the ignition, with the engine OFF.
- Attempt to start the engine, then release the key to ON (vehicle will not start).
- Observe the SECURITY light, after approximately 10 minutes the light will turn OFF.
- Turn OFF the ignition, and wait 10 seconds.
- Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes ( the vehicle
- is now ready to relearn the Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).
Important: The vehicle relearns Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
Start the engine (the vehicle has now learned the Sensor Data Code and/or password).