You have a standard GM passlock system, as you turn the key you are rotating a magnet past a stationary Hall Effect sensor at the ignition lock cylinder. You didn’t say if your vehicle actually starts and runs. If it does run after waiting a few minutes then the passlock system is in "long tamper mode". If the engine doesnt start then the passlock has gone into "lock out mode". Lack of information from the key or ignition lock sensor to the passlock computer will set passlock system DTCs (codes) and will keep the security lamp on until the codes are dealt with or cleared.