Here is more about SKIS:
08 - Electrical / 8Q - Vehicle Theft Security / Operation
SENTRY KEY IMMOBILIZER SYSTEM
The Sentry Key Immobilizer System (SKIS) is designed to provide passive protection against unauthorized vehicle use by disabling the engine after about two seconds of running whenever an attempt is made to operate the vehicle using anything other than a key or FOB with Integrated Key (FOBIK) equipped with a valid Sentry Key transponder microchip. The SKIS is considered a passive protection system because it is always active when the ignition system is energized and does not require any customer intervention.
The Radio Frequency Hub Module (RFHM) uses Radio Frequency (RF) communication to challenge and obtain confirmation that the FOBIK being used is valid for operating the vehicle. The microcontroller-based RFHM hardware and software also uses electronic messages to communicate with the ignition switch (also known as the Keyless Ignition Node/KIN on vehicles with Passive Entry Keyless Go/PEKG or IGnition Node Module/IGNM on vehicles without PEKG) over a private serial bus and with other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. (Refer to 08 - Electrical/8E - Electronic Control Modules/COMMUNIPCATION - Operation) .
Pre-programmed Sentry Key transponder-equipped keys or FOBIK units are provided with the vehicle from the factory. Each RFHM will recognize a maximum of eight Sentry Key FOBIK units. If the customer would like additional Sentry Key FOBIK units other than those provided with the vehicle, they may be purchased from any authorized dealer. These additional FOBIK units must be programmed to the RFHM in the vehicle in order for the system to recognize them as valid. This can be done by the dealer using a diagnostic scan tool.
In vehicles with a rotary ignition switch the RFHM controls Low Frequency (LF) signaling with the Sentry Key transponder integral to the mechanical key or FOB with Integrated Key (FOBIK) through a tuned antenna internal to the IGNM. The IGNM transmits the received LF signal and the selected ignition switch status back to the RFHM. In vehicles with the push button PEKG system, the RFHM transmits LF signals to, and receives LF signals from the Sentry Key transponder integral to the FOBIK through a tuned antenna internal to the RFHM housing, while the KIN allows the vehicle operator to select and monitor the status of the ignition switch and also transmits the selected ignition switch status back to the RFHM.
The RFHM also serves as the Remote Keyless Entry (RKE) RF receiver and, if the vehicle is so equipped, the receiver for the remote start system and for the Tire Pressure Monitoring (TPM) system. The RFHM communicates over the Controller Area Network (CAN) data bus with the Body Control Module (BCM), the Instrument Panel Cluster (IPC), the Powertrain Control Module (PCM) or the diagnostic scan tool. It also communicates over a dedicated Local Interface Network (LIN) data bus circuit with the IGNM or the KIN.
The RFHM 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 RFHM or the PCM. However, the use of this strategy also means that replacement of either the RFHM or the PCM units will require a system initialization procedure to restore system operation.
The RFHM retains in memory the ID numbers of any Sentry Key or FOBIK transponder that is programmed into it. A maximum of eight Sentry Key transponders can be programmed into the RFHM. For added system security, each RFHM is programmed with a unique Secret Key code. This code is stored in memory, sent over the CAN data bus to the PCM, and is encoded to the transponder of every Sentry Key that is programmed into the RFHM. Therefore, the Secret Key code is a common element that is found in every component of the SKIS.
Another security code called a PIN is used to gain access to the RFHM Secured Access Mode. The Secured Access Mode is required during service to perform the SKIS initialization and Sentry Key transponder programming procedures. The RFHM also stores the Vehicle Identification Number (VIN) in its memory, which it learns through a CAN data bus message from the PCM during SKIS initialization.
In the event that a RFHM replacement is required, the Secret Key code can be transferred to the new RFHM from the PCM using the diagnostic scan tool and the SKIS initialization procedure. Proper completion of the SKIS initialization will allow the existing Sentry Key transponder units to be programmed into the new RFHM so that new Sentry Key units will not be required. In the event that the original Secret Key code cannot be recovered, RFHM replacement will also require new Sentry Key units. The diagnostic scan tool will alert the technician during the SKIS initialization procedure if new Sentry Key units are required. (Refer to 08 - Electrical/8E - Electronic Control Modules - Standard Procedure) .
When the status of the ignition switch transitions to On, the RFHM transmits a LF signal to excite the transponder in the FOBIK. The RFHM then waits for a LF signal response from the transponder. If the response received identifies the key or FOBIK as valid, the RFHM sends an electronic valid key message to the PCM over the CAN data bus. If the response received identifies the key or FOBIK as invalid or if no response is received from the key or FOBIK transponder, the RFHM sends an invalid key message to the PCM. The PCM will enable or disable engine operation based upon the status of the RFHM messages. It is important to note that the default condition in the PCM is an invalid key; therefore, if no message is received from the RFHM by the PCM, the engine will be disabled and the vehicle immobilized after two seconds of running.
The RFHM also sends electronic security indicator request messages to the IPC over the CAN data bus to tell the IPC how to operate the security indicator. The security indicator request message from the RFHM tells the IPC to turn the indicator On for about three seconds each time the status of the ignition switch transitions to On as a bulb test. After completion of the bulb test, the RFHM sends security indicator request messages to the IPC to turn the indicator Off, turn the indicator On or to flash the indicator On and Off. If the security indicator flashes or stays On solid after the bulb test, it signifies a SKIS fault. If the RFHM detects a system malfunction or the SKIS has become ineffective, the security indicator will stay On solid. If the RFHM detects an invalid key or FOBIK, or if a key or FOBIK transponder-related fault exists, the security indicator will flash.
The RFHM performs a self-test of the SKIS each time the status of the ignition switch transitions to ON, and will store fault information in the form of a Diagnostic Trouble Code (DTC) for any system or component malfunction that is detected. If a fault is detected, the RFHM will send an electronic security indicator request message to the IPC and the IPC will illuminate the security indicator as appropriate.
The hard wired circuits between components related to the SKIS may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin out information and location views for the various wire harness connectors, splices and grounds.
However, conventional diagnostic methods will not prove conclusive in the diagnosis of the SKIS or the electronic controls and communication between other modules and devices that provide some features of the SKIS. The most reliable, efficient and accurate means to diagnose the SKIS or the electronic controls and communication related to SKIS operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.
Key looks like this:
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