Antitheft and Alarm Systems: Description and Operation
VEHICLE THEFT SECURITY SYSTEMThe Vehicle Theft Security System (VTSS) is designed to protect against whole vehicle theft. The system monitors vehicle doors, deck lid key cylinder, and ignition action for unauthorized operation. The alarm activates:
- Sounding of the horn
- Flashing of the park and tail lamps
- Flashing of the headlamps
- An engine kill feature (without SKIS)
Upon failure of proper VTSS/SKIM communication to the PCM, the PCM will shut off fuel after two seconds of run time. The engine will not re-crank on the key cycle that the failure occurred, a full key down sequence must be performed for the engine to crank again. After six consecutive fuel shut-offs, the engine will no longer crank on subsequent key cycles. The failure must be corrected and a valid communication process between the BCM (VTSS), or SKIM, and the PCM must occur for the engine to crank and start again.
The electronics for the VTSS are part of the Body Control Module (BCM). The system is armed when the vehicle is locked using the:
- Power door lock switches
- Remote Keyless Entry transmitter.
For vehicles equipped with SKIS, the doors do not have to be locked to enable the fuel shut off feature.
After the vehicle is locked and the last door is closed, the set LED indicator in the top cover will flash quickly for 16 seconds, indicating that arming is in progress. If no monitored systems are activated during this period, the system will arm. After 16 seconds the indicator LED will continue to flash at a slower rate.
This indicates that the system is armed. If the deck lid key cylinder switch is not sensed by the system, the indicator LED will remain lit during the arming process, although the system will still arm. If the indicator LED does not illuminate at all upon door closing it indicates that the system is not arming.
Passive disarming occurs upon normal vehicle entry by unlocking either door with the ignition key/remote transmitter. This disarming will also halt the alarm once it has been activated.
A tamper alert exists to notify the driver that the VTSS had been activated. This alert consists of 3 horn pulses when the vehicle is disarmed.
The VTSS will not arm by pushing down the door lock mechanism. This will manually override the system.
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. The components of this system are the Sentry Key Immobilizer Module (SKIM), Body Control Module (BCM), Sentry Key transponder, 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 panel top cover.
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 Body Diagnostic Procedures.
SKIS OPERATION
When ignition power is supplied to the SKIM, the SKIM performs an internal self-test. After the self- test is completed, the SKIM energizes the antenna (this activates the transponder chop responds to the challenge by generating an encrypted response message using the following:
Secret Key - This is an electronically stored value (identification number) that is unique to each SKIS. The secret key is stored in the SKIM, PCM and all ignition key transponders.
Challenge - This is a random number that is generated by the SKIM at each ignition key cycle.
The secret key and challenge are the two variables used in the algorithm that produces the encrypted response message. The transponder uses the crypto algorithm to receive, decode and respond to the message sent by the SKIM. After responding to the coded message, the transponder sends a transponder ID message to the SKIM. The SKIM compares the transponder ID to the available valid key codes in the SKIM memory (8 key maximum at any one time). After validating the key the SKIM sends a PCI Bus message called a "Seed Request" to the engine controller then waits for a PCM response. If the PCM does not respond, the SKIM will send the seed request again. After twenty failed attempts the SKIM will stop sending the seed request and store a trouble code. If the PCM sends a seed response, the SKIM sends a valid/invalid key message to the PCM. This is an encrypted message that is generated using the following:
VIN - Vehicle Identification Number
Seed - This is a random number that is generated by the PCM at each ignition key cycle.
The VIN and seed are the two variables used in the rolling code algorithm that encrypts the "valid/invalid key" message. The PCM uses the rolling code algorithm to receive, decode and respond to the valid/invalid key message sent by the SKIM. After sending the valid/invalid key message the SKIM waits 3.5 seconds for a PCM status message from the PCM. If the PCM does not respond with a valid key message to the SKIM, a fault is detected and a trouble code is stored.
The SKIS incorporates a warning lamp located on the instrument panel upper cover. The lamp receives switched ignition voltage and is hardwired to the body control module. The lamp is actuated when the SKIM sends a PCI Bus message to the body controller requesting the lamp ON. The body controller then provides the ground for the lamp. The SKIM will request lamp operation for the following:
- bulb checks at ignition ON
- to alert the vehicle operator to a SKIS malfunction
For all faults except transponder faults the lamp remains ON steady. In the event of a transponder fault the light flashes at a rate of 1 Hz (once per second). If a fault is present the lamp will remain ON or flashing for the complete ignition cycle. If a fault is stored in SKIM memory which prevents the system from operating properly, the PCM will allow the engine to start and run (for 2 seconds) up to six times. After the sixth attempt, the PCM disables the starter relay until the fault is corrected.
SENTRY KEY IMMOBILIZER MODULE (SKIM)
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.
Sentry Key Immobilizer Module Location:
Sentry Key Immobilizer Module:
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 8 mm (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 and sends the code over the PCI bus to the PCM, which also keeps this code in its 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 BCM which controls the VTSS indicator LED. The SKIM sends messages to the BCM to turn the LED 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 LED off for a duration of about one second. Then the SKIM sends messages to turn the LED on or off based upon the results of the SKIS self-tests. If the VTSS indicator LED 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 LED. The SKIM can also send messages to flash the LED and to generate a single audible chime tone. These functions 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 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 Body Diagnostic Procedures 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 LED to give an indication when the SKIS is faulty or when the vehicle has been immobilized due to the use of an invalid ignition key. The LED is controlled by the BCM based upon messages received from the Sentry Key Immobilizer Module (SKIM). The VTSS/ SKIS indicator LED is hard wired directly to the BCM.
The SKIM sends messages to the BCM to turn the LED 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 the BCM to keep the LED off for a duration of about one second. Then the SKIM sends messages to the BCM to turn the LED on or off based upon the results of the SKIS self-tests. If the VTSS indicator LED 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 the BCM to flash the VTSS indicator LED.
The SKIM can also send messages to the BCM to flash the LED and to generate a single audible chime tone. These functions 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 for more information on the "Customer Learn" programming mode.
The VTSS indicator LED is housed in the Automatic Temperature Control (ATC) Sun Sensor located in the instrument panel top cover. Refer to Instrument Panel and Systems for service of ATC Sun Sensor. If the VTSS indicator LED comes on and stays on after the bulb test function, diagnosis of the SKIS should be performed with a DRB III scan tool and the proper Body Diagnostic Procedures.
SENTRY KEY IMMOBILIZER TRANSPONDER
Sentry Key Immobilizer Transponder:
The Sentry Key Immobilizer System (SKIS) uses a transponder that is integral to each of two ignition key that are supplied with the vehicle when it is shipped from the factory. The transponder chip is insulated within a nylon mount inserted in the head of the key, and invisible beneath a molded rubber cap.
Each Sentry Key transponder has a unique transponder identification code programmed into it by the manufacturer. The Sentry Key Immobilizer Module (SKIM) has a unique "Secret Key" code programmed into it by the manufacturer. When a Sentry Key transponder is programmed into the memory of the SKIM, the SKIM learns the transponder identification code from the transponder, and the transponder learns the "Secret Key" code from the SKIM. Each of these codes is stored within the transponder and in the nonvolatile memory of the SKIM. Therefore, blank keys for the SKIS must be programmed by and into the SKIM, in addition to being cut to match the mechanical coding of the ignition lock cylinder. See Sentry Key Immobilizer System Transponder Programming for more information.
The Sentry Key transponder is within the range of the SKIM transceiver antenna ring when it is inserted in the ignition lock cylinder. When the ignition switch is turned to the START or ON positions, the SKIM transceiver issues a Radio Frequency (RF) signal that excites the transponder chip. The transponder chip responds by issuing an RF signal containing its transponder identification code and the "Secret Key" code. The SKIM transceiver compares the transponder codes with the codes stored in its memory to determine whether a valid key is in the ignition lock cylinder.
The Sentry Key transponder cannot be repaired and, if faulty or damaged, it must be replaced.
SKIM ON-BOARD DIAGNOSTICS
The SKIM has been programmed to transmit and monitor many different coded messages as well as PCI Bus messages. This monitoring is called "On Board Diagnosis"
Certain criteria must be met for a diagnostic trouble code to be entered into the SKIM memory. The criteria may be a range of; Input voltage, PCI Bus message, or coded messages to the SKIM. If all of the criteria for monitoring a circuit or function are met and a fault is sensed, a diagnostic trouble code will be stored in the SKIM memory.
TRIGGERING THE VTSS
Any of the following actions will trigger the system:
1. Opening any door.
2. Removing the deck lid lock cylinder.
3. Turning the ignition to the ON position.
Using the power door switch or the keyless transmitter will arm the system.
CAUTION: The VTSS indicator LED will trigger and engine will continue to run if the vehicle is equipped with SKIS and the proper key is used to start the vehicle. This condition will occur if the VTSS has been triggered.
NOTE: The ignition switch can be turned to the accessory position without triggering alarm system.