I changed the ignition cylinder and the theft system. will not let the car stay started how to fix the problem ..

Are you the one who bought the vehicle new ? Replaced ignition switch or the ignition lock cylinder ? No , sorry, but a remote start will not by pass anti-theft system .

The vehicle theft deterrent system is designed in order to prevent vehicle theft by disabling the fuel injectors unless the lock cylinder is correctly engaged by a mechanical key. The theft deterrent system uses the following 4 components for theft prevention:
• The lock cylinder
• The ignition switch
• The body control module (BCM)
• The powertrain control module (PCM)
When starting the engine, the PCM searches for a password from the BCM through the Class 2 serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. Two modes of tamper detection are provided:
No password received
The engine will start and stall quickly. SECURITY telltale will flash on the instrument panel cluster (IPC) and then stay ON steady.
Incorrect or disable password received (More than 3 invalid passwords are received)
The engine is disabled for at least 10 minutes and the SECURITY telltale will illuminate solid on the IPC during the 10 minutes.
After the vehicle has passed theft detection, the PCM will continue normal operation.

You can't do that an expect the vehicle to start , software programmed in the computer system . If the engine PCM doesn't see a pass word or coded message from the BCM or anti-theft module . IT will disable starting and or fuel injetor control .
Important: Due to component variability, the vehicle theft deterrent (VTD) system must have the learn procedure performed regardless, if the vehicle starts on the first ignition cycle after a VTD repair.
All codes in the theft deterrent module must be cleared for a relearn.
The vehicle theft deterrent system is designed in order to prevent vehicle theft by disabling the fuel injectors unless the lock cylinder is correctly engaged by a mechanical key. The theft deterrent system uses the following 4 components for theft prevention:
• The lock cylinder
• The ignition switch
• The body control module (BCM)
• The powertrain control module (PCM)
When starting the engine, the PCM searches for a password from the BCM through the Class 2 serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. Two modes of tamper detection are provided:
• No password received
The engine will start and stall quickly. SECURITY telltale will flash on the instrument panel cluster (IPC) and then stay ON steady.
• Incorrect or disable password received (More than 3 invalid passwords are received)
The engine is disabled for at least 10 minutes and the SECURITY telltale will illuminate solid on the IPC during the 10 minutes.
After the vehicle has passed theft detection, the PCM will continue normal operation.

They do sell by pass modules you can find on the internet , in some cases it cheaper to have it fixed proper by a qualified repair shop . It just depends what the original problem was . You how ever just complicated matters by changing thing's .

You have two choices. You can either change out your ignition lock cylinder with a new one and have a locksmith change the pins so your original key works with it. Or you can get your car to a mobile audio shop that installs remote start systems and have them bypass your VATSS system.

There is a problem with the system an there is a DTC - diagnostic trouble code stored in the body control module !
The vehicle theft deterrent system is designed in order to prevent vehicle theft by disabling the fuel injectors unless the lock cylinder is engaged by the correct mechanical key. The theft deterrent system uses the following 4 components for theft prevention:
?€¢
The lock cylinder

?€¢
The ignition switch

?€¢
The body control module (BCM)

?€¢
The powertrain control module (PCM)

When starting the engine, the PCM searches for a password from the BCM through the Class 2 serial data circuit. If the password is not recognized or not present, the PCM will disable the fuel injectors. Two modes of tamper detection are provided:
?€¢
No password received

The engine will start and stall quickly. SECURITY telltale will flash on the instrument panel cluster (IPC) and then stay ON steady.

?€¢
Incorrect or disable password received (More than 3 invalid passwords are received)

The engine is disabled for at least 10 minutes and the SECURITY telltale will illuminate solid on the IPC during the 10 minutes.

After the vehicle has passed theft detection, the PCM will continue normal operation
Ignition Switch
The mechanical key and lock cylinder is located on the steering column. The main electrical switching portion of the assembly is separate from the key and lock cylinder. The VTD portion of the ignition switch is the Passlock?"¢ cylinder.
The Passlock?"¢ lock cylinder is a locking cylinder that turns a magnet past a stationary hall effect sensor. When turned to crank, the hall effect sensor is latched which applies a fixed resistance to the Passlock?"¢ signal data circuit. The voltage measured by the BCM on the Passlock?"¢ signal data circuit is the Passlock?"¢ data value.
Body Control Module (BCM)
The BCM compares the Passlock?"¢ data value to a value that it has stored in memory. If the values match the BCM sends a password via the class 2 serial data line to the PCM.
Powertrain Control Module (PCM)
When the PCM receives the correct password, the PCM enables the fuel injection system, allowing the vehicle to operate correctly. The PCM may allow the car to start and quickly stall during a failed theft condition.
If the BCM does not receive a Passlock?"¢ data value, the BCM will enter a short tamper mode. During this mode, the VTD system will not allow the car to operate for 4 seconds.
If the Passlock?"¢ data value is incorrect, the VTD system will enter the long tamper mode. In the long tamper mode, the following actions will occur:
?€¢
The THEFT SYSTEM indicator will flash.

?€¢
The fuel injectors will be shut off for approximately 10 minutes.

Although the vehicle may start, the engine will quickly stall due to a fuel cut-off.
In the event of an open in the serial data communication between the BCM and the PCM or a failure in the Passlock?"¢ lock cylinder, the following actions occur:
?€¢
The VTD system will become fail-enabled if the car has already passed theft for that ignition cycle (i.e. the engine is running).

?€¢
The PCM or the BCM may set diagnostic trouble codes (DTCs).

?€¢
The THEFT SYSTEM indicator will light continuously.

?€¢
The PCM will become fail-enabled for future ignition cycles.

If a failure occurs when the ignition is off, while the VTD system is not fail-enabled, the PCM will never receive a valid password, and will not allow vehicle operation by disabling the fuel injectors. An this system can set 6 DTC'S
DTC B2947 Security System Sensor Power CKT Low DTC B2948 Security System Sensor Power CKT High DTC B2957 Security System Sensor Data Circuit Low DTC B2958 Security System Sensor Data Circuit High DTC B2960 Sec Sys Sensor Data Incorrect but Valid DTC B3031 Security System Controller in Learn Mode DTC B3033 Security System Indicates Tamper

The security, antitheft, or passlock light 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 misinterperates 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 may help you find ways to bypass this or fix it yourself.
http://vatspasslockpasskeysecurityhelp.yolasite.com/

problem in theft security system it has to be reprogrammed to new key new ignition switch key lock system. dealership fix need diagnostic eqquipment to reprogram new ignition key and ignition switch lock cylinder to the immobilizer control module and ECM.

When the motor was replaced , was the original PCM changed as well ? Did you have the anti-theft system programmed . Theft - system light on -DTC'S - diagnostic trouble codes are stored . Need a factory or professional scan tool read these codes . The other computers on the vehicle will communicate . BCM
Important: Due to component variability, the vehicle theft deterrent (VTD) system must have the learn procedure performed regardless, if the vehicle starts on the first ignition cycle after a VTD repair.
All codes in the theft deterrent module must be cleared for a relearn.
The vehicle theft deterrent system is designed in order to prevent vehicle theft by disabling the fuel injectors unless the lock cylinder is correctly engaged by a mechanical key. The theft deterrent system uses the following 4 components for theft prevention:
• The lock cylinder
• The ignition switch
• The body control module (BCM)
• The powertrain control module (PCM)
When starting the engine, the PCM searches for a password from the BCM through the Class 2 serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. Two modes of tamper detection are provided:
• No password received
The engine will start and stall quickly. SECURITY telltale will flash on the instrument panel cluster (IPC) and then stay ON steady.
• Incorrect or disable password received (More than 3 invalid passwords are received)
The engine is disabled for at least 10 minutes and the SECURITY telltale will illuminate solid on the IPC during the 10 minutes.
After the vehicle has passed theft detection, the PCM will continue normal operation.

DTC B2947 Security System Sensor Power CKT Low
DTC B2948 Security System Sensor Power CKT High
DTC B2957 Security System Sensor Data Circuit Low
DTC B2958 Security System Sensor Data Circuit High
DTC B2960 Invalid Coded Key Present
DTC B3031 Key Decoder Device in Assem Learn Mode
DTC B3033 Security System Indicates Tamper

Does pin # 16 at the DLC have B+ voltage ?

when we try to start the car it will not stay running are theft system stay on how can can we fix it

SOUND LIKE THE THEFT SECURITY PROBLEMS. MOST OF THE TIME.THE IGNITION KEYS OR IGNITION SWITCH KEY LOCK CYLINDER WORN WHERE THE BCM AND PCM DONT RECOGNIZE KEY OR SWITCH SIGNAL.SO THE BCM AND PCM WILL GO IN THEFT SECURITY MODE.THE DEALERSHIP WILL HAVE TO FIX.BECAUSE IF THE KEYS , IGNITION SWITCH AND LOCK CYLINDER AND BCM HAS TO REPLACED.THEY WILL HAVE TO BE REPROGRAM USING DIAGNOSTIC EQUIPMENT. NOT A HOME FIX.YOU WILL NEED TO GET FIX SOON AS POSSIBLE.BECAUSE FAULTY SECURITY THEFT CODE WILL SHUT DOWN VECHICLE FUEL SYSTEM WHILE DRIVING OR IT WILL GET TO A POINT WHERE CAR WONT START NO MORE.THIS FIX WILL COST ABOUT $600.00.

no enciende el coche, en el tablero esta pendiendo y apagando la luz de theft system. que puedo hacer para que funcione el coche