How can the security passcode be removed

Hi: I am very familiar with this! Not a mechanic though. Turn off all accessories, ie, radio, air/heat, etc. Turn the key to ACC and let the security light flash for 8 minutes. During this time, don't open doors, or do anything electronic or it will have to start the reset all over. Once it stops flashing, turn key to off, then turn to start. It should clear the problem for a few days, a few weeks, or even a month. There is a bypass kit for this issue but from what I'm told, the GM dealership charges an arm and a leg. Hope this solves your problem.

It could be a your passlock II anti theft ignition. This is the complete relearn procedure, it should reset in 10 mins. but could take a little more than 30 minutes but easy to do. Your ignition has 4 positions 1.Off 2.ACC 3.On 4.Start (Cranks over & springs back to 3.On) Step 1 – Attempt to start the vehicle, this is the "start" position. It will crank, and start for 1-2 seconds then stall. The security light will be on or flashing. Leave the key in the ‘on’ position for 10-11 minutes, then the security light will stay solid or go off. Step 2 – Turn the key to the ‘off’ position for no less 10 seconds. Attempt to start the vehicle. If it runs at this point then you have reset your passlock. If the problem persists you can continue repeat Step 1 two more times. Make sure turn the key to the ‘off’ position for 10 seconds before each 10 minute cycle. Hopefully your car is running by now Step 3 – The vehicle is now ready to relearn the proper code. Turn the key ‘off’ for 15 seconds and then ‘crank’ the vehicle. it should start back up now. The security light might stay on solid for several minutes afterwards.