My ignition switch is bad so I changed it now how do I reset the anti-theft system so the car will start

check for worn --damaged key-- ignition cylinder --ignition switch

There is no way to reset the "Anti-Theft" system. Hopefully you have more than one ignition key. Slide one key into the ignition cylinder and try to start the engine. If nothing, try the same thing with the other key. There is a transponder inside each key and the exciter ring will send a signal to the key. If the signal that it receives is not valid, then the Anti-Theft system will tell the ECU not to allow the car to be started. What is the security light doing while you try to start the engine? Did this problem happen out of the blue? Was a repair performed on the ignition switch? Are there any other symptoms? Please write back and let me know, good luck.

Here are two methods to reset the anti-theft system on 2007 Chevy Malibu:
1st method
1. Put the ignition in on position, let it breathe for 10 minutes, and remove it when the anti-theft system light stops blinking.
2. Crank up the engine; it should now start
2nd method
• While outside the car, press and hold the lock and unlock button together
• Let go when the car honks and the lights flash
• Put the key in the ignition and rotate to the ON position, and leave there for 30 seconds
• Switch on the car, and the anti-theft system would have reset

TURN ON IGNITION SWITCH TO ON POSITION.ENGINE OFF.REPEATEDLY PRESS VECHICLE INFORMATION BUTTON UNTIL PRESS TO RELEARN REMOTE KEY IS DISPLAYED.PRESS SET RESET BUTTON UNTIL REMOTE KEY LEARNING ACTIVE IS DISPLAYED. IF THAT PROCEDURE DONT WORK.INSERT MASTER KEY INTO IGNITION SWITCH.NOW SWITCH IGNITION ON SWITCH IGNITION OFF.REMOVE MASTER KEY.WITHIN 10 SECONDS INSERT NEW KEY.SWITCH IGNITION ON.ENSURE SYSTEM WARNING LAMP SWITCHES OFF.NEW KEY NOW PROGRAMMED.IF YOU STILL HAVING PROBLEM RESETING THEFT SECURITY SYSTEM THE DEALERSHIP HAS TO FIX.REPROGRAM IT.

Good Evening, your anti-theft is in the ignition. If you go to start the car, then leave the key in the run position when it does not start for about 11- 15mins. Once the security light goes off then turn it off and try starting it. If it does not work you might have to do it a couple more times. What happens is the system relearns your key. Hope that helps,
Thanks,
Joey

Place key in ignition, turn to ON position. (do not start)
Leave in ON position for EXACTLY 10 minutes.
As SOON as the anti-theft light turns off, then IMMEDIATELY start the car.
Then anti-theft is now reset.

Sounds like a bad ignition switch have ur body control module checked for codes if u have a B2960 and or B3033 then replace the ignition switch.

SECURITY
If your vehicle has the remote keyless entry system, this feature allows you to select the method used to arm the vehicle's security system. When SECURITY appears on the display, press the reset button to scroll through the available settings:
* RKE (Remote Keyless Entry) (default): The content theft-deterrent system will arm when the lock button on the remote keyless entry transmitter is pressed or when the power door lock switch is pressed.

* PASSIVE: The content theft-deterrent system will arm itself 60 seconds after the ignition has been turned off and all of the doors have been closed.


Hopd this help (remember comment and rated this).