Antitheft and Alarm Systems: Description and Operation

VEHICLE THEFT SECURITY SYSTEM
The Vehicle Theft/Security System (VTSS) is designed to protect against whole vehicle theft. The system monitors the vehicle doors and ignition for unauthorized operation.

The VTSS activates:
- Sounding of the horn
- Flashing of the park lamps
- Flashing of the head lamps

The Remote Keyless Entry (RKE) has 1 mode of operation, CUSTOMER USAGE mode. The customer usage mode provides full functionality of the module and is the mode in which the RKE module should be operating when used by the customer.

When in the Customer Usage mode of operation, the system is armed when the vehicle is locked using the:
- Power Door Lock Switches
- Remote Keyless Entry (RKE) Transmitter
- Key Cylinder Switches

After the vehicle is locked and the last door is closed, the VTSS indicator in the instrument cluster will flash quickly for 16 seconds, indicating that the arming is in process. After 16 seconds, the LED will continue to flash at a slower rate indicating that the system is armed.

VTSS disarming occurs upon normal vehicle entry by unlocking either door via the key cylinder or RKE transmitter, or by starting the vehicle with a valid Sentry Key. This disarming will also halt the alarm once it has been activated.

A tamper alert exists to notify the driver that the system has been activated. This alert consists of 3 horn pulses and the security telltail flashing for 30 seconds when the vehicle is disarmed. The tamper alert will not occur if disarmed while alarming.

The VTSS will not arm by mechanically locking the vehicle doors. This will manually override the system.

The Alarming state will last for 18 minutes after which it will timeout and return to the armed state. A tamper alert feature will alert the customer to the alarm being tripped while they were away upon returning to the vehicle by flashing the VTSS indicator for 30 seconds after the system has been disarmed.

All of the switches for the VTSS system can be monitored using the DRB III. The DRB III is also useful for a customer complaint of the alarm going OFF with no apparent reason by viewing the VTSS last alarm caused by display.

Sentry Key Immobilizer System (SKIS)
The Sentry Key Immobilizer System (SKIS) is designed to provide passive protection against unauthorized vehicle use by preventing the engine from operating while the system is armed. The primary components of this system are the Sentry Key Immobilizer Module (SKIM), the Sentry Key transponder, the Vehicle Theft/Security System (VTSS) indicator LED, and the Powertrain Control Module (PCM).

The SKIM is installed on the steering column near the ignition lock cylinder. The transponder is located under the molded rubber cap on the head of the ignition key The VTSS indicator LED is located in the instrument cluster.

The SKIS includes two valid Sentry Key transponders from the factory. This is so the customer can self program new keys if one is lost. If the customer wishes, additional non-coded blank Sentry Keys are available. These blank keys can be cut to match a valid ignition key, but the engine will not start unless the key transponder is also programmed to the vehicle. The SKIS will recognize no more than eight valid Sentry Key transponders at any one time. The SKIS performs a self-test each time the ignition switch is turned to the ON position, and will store Diagnostic Trouble Codes (DTC's) if a system malfunction is detected. The SKIS can be diagnosed, and any stored DTC can be retrieved using a DRB III scan tool as described in the proper Body Diagnostic Procedures Manual.

The SKIS includes two valid Sentry Key transponders from the factory These two Sentry Keys can be used to program additional non-coded blank Sentry Keys. These blank keys can be cut to match a valid ignition key but the engine will not start unless the key transponder is also programmed to the vehicle. The SKIS will recognize no more than eight valid Sentry Key transponders at any one time.

The SKIS performs a self-test each time the ignition switch is turned to the ON position, and will store Diagnostic Trouble Codes (DTC's) if a system malfunction is detected. The SKIS can be diagnosed, and any stored DTC can be retrieved using a DRB III scan tool as described in the proper Powertrain Diagnostic Procedures manual.

Sentry Key Immobilizer Module
The Sentry Key Immobilizer Module (SKIM) contains a Radio Frequency (RF) transceiver and a central processing unit, which includes the Sentry Key Immobilizer System (SKIS) program logic. The SKIS programming enables the SKIM to program and retain in memory the codes of at least two, but no more than eight electronically coded Sentry Key transponders. The SKIS programming also enables the SKIM to communicate over the Programmable Communication Interface (PCI) bus network with the Powertrain Control Module (PCM), and/or the DRB III scan tool.

The SKIM transmits and receives RF signals through a tuned antenna enclosed within a molded plastic ring formation that is integral to the SKIM housing. When the SKIM is properly installed on the steering column, the antenna ring is oriented around the circumference of the ignition lock cylinder housing. This antenna ring must be located within eight millimeters (0.31 inches) of the Sentry Key in order to ensure proper RF communication between the SKIM and the Sentry Key transponder.

For added system security each SKIM is programmed with a unique "Secret Key" code and a security code. The SKIM keeps the "Secret Key" code in memory The SKIM also sends the "Secret Key" code to each of the programmed Sentry Key transponders. The security code is used by the assembly plant to access the SKIS for initialization, or by the dealer technician to access the system for service. The SKIM also stores in its memory the Vehicle Identification Number (VIN), which it learns through a PCI bus message from the PCM during initialization.

The SKIM and the PCM both use software that includes a rolling code algorithm strategy, which helps to reduce the possibility of unauthorized SKIS disarming. The rolling code algorithm ensures security by preventing an override of the SKIS through the unauthorized substitution of the SKIM or the PCM. However, the use of this strategy also means that replacement of either the SKIM or the PCM units will require a system initialization procedure to restore system operation.

When the ignition switch is turned to the ON or START positions, the SKIM transmits an RF signal to excite the Sentry Key transponder. The SKIM then listens for a return RF signal from the transponder of the Sentry Key that is inserted in the ignition lock cylinder. If the SKIM receives an RF signal with valid "Secret Key" and transponder identification codes, the SKIM sends a "valid key" message to the PCM over the PCI bus. If the SKIM receives an invalid RF signal or no response, it sends "invalid key" messages to the PCM. The PCM will enable or disable engine operation based upon the status of the SKIM messages.

The SKIM also sends messages to the Instrument Cluster which controls the VTSS indicator. The SKIM sends messages to the Instrument Cluster to turn the indicator ON for about three seconds when the ignition switch is turned to the ON position as a "bulb" test. After completion of the "bulb" test, the SKIM sends bus messages to keep the indicator OFF for a duration of about one second. Then the SKIM sends messages to turn the indicator ON or OFF based upon the results of the SKIS self-tests. If the VTSS indicator comes ON and stays ON after the "bulb test", it indicates that the SKIM has detected a system malfunction and/or that the SKIS has become inoperative.

If the SKIM detects an invalid key when the ignition switch is turned to the ON position, it sends messages to flash the VTSS indicator. The SKIM can also send messages to flash the indicator to serve as an indication to the customer that the SKIS has been placed in its "Customer Learn" programming mode. See Sentry Key Immobilizer System Transponder Programming in this section for more information on the "Customer Learn" programming mode.

For diagnosis or initialization of the SKIM and the PCM, a DRB III scan tool and the proper Powertrain Diagnostic Procedures manual are required.

The SKIM cannot be repaired and, if faulty or damaged, the unit must be replaced.

SENTRY KEY IMMOBILIZER SYSTEM INDICATOR LAMP
The Sentry Key Immobilizer System (SKIS) uses the Vehicle Theft Security System (VTSS) indicator in the instrument cluster to give an indication when the SKIS is faulty or when the vehicle has been immobilized due to the use of an invalid key The indicator is controlled by the instrument cluster based upon messages received from the Sentry Key Immobilizer Module (SKIM).

The SKIM sends PCI Bus messages to the instrument cluster, to turn on the "Security" indicator for about 3 seconds when the ignition is turned to the ON position, as a "Bulb" test. After completion of the "Bulb" test, the SKIM sends a PCI bus messages to keep the LED OFF for 1 second. Then the SKIM sends messages to the instrument cluster to turn the LED off based upon the results if the SKIS self - test. If the indicator illuminates and remains illuminated after the "bulb test , it indicates that the SKIM has detected a system malfunction and/or the system has become inoperative. If the SKIM detects a invalid key when the ignition switch is turned on, it sends a message to the instrument cluster to flash the "Security" indicator.

The SKIM can also send messages to the cluster to flash the LED and generate a chime. These functions serve as an indication to the customer that the SKIM is in the Customer Learn programming mode. See Sentry Key Immobilizer System Transponder Programming in this group for more information on the "Customer Learn" programming Mode.

If the VTSS indicator remains on after the "Bulb" test, the system should be diagnosed using the DRB III scan tool and the proper Powertrain Diagnostic Procedures manual.