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 any method other than a valid Sentry Key FOB with Integrated Key (FOBIK) is used to start the vehicle. 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 SKIS uses Low Frequency (LF) Radio Frequency (RF) communication to obtain confirmation that the FOBIK is valid for operating the vehicle.
The microcontroller-based Radio Frequency Hub (RFH) contains the SKIS software. The RFH uses electronic messages over a dedicated Local Interface Network (LIN) data bus to communicate with the ignition switch (Keyless Ignition Node/KIN) and also uses electronic messages to communicate with other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. The RFH contains a Radio Frequency (RF) transceiver and a microcontroller. The RFH transmits Low Frequency (LF) signals to, and receives LF signals from the Sentry Key transponder integral to the FOBIK through a tuned antenna internal to the RFH housing. The KIN allows the vehicle operator to select and monitor the status of the ignition switch and also transmits the selected ignition switch status to the RFH. Refer to COMMUNICATION, OPERATION .
Pre-programmed Sentry Key FOBIK transponders are provided with the vehicle from the factory. Each RFH will recognize a maximum of eight Sentry Key FOBIK transponders. If the customer would like additional 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 RFH 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. All FOBIK units authorized for use in a given vehicle must be present in the vehicle when programming takes place in order to remain valid. Refer to STANDARD PROCEDURE .
The RFH also serves as the Remote Keyless Entry (RKE) RF receiver and, if the vehicle is so equipped, the receiver for the remote start system. Refer to REMOTE KEYLESS ENTRY SYSTEM . The RFH communicates over the 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 KIN.
The RFH 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 RFH or the PCM. However, the use of this strategy also means that replacement of either the RFH or the PCM units will require a system initialization procedure to restore system operation.
The RFH retains in memory the ID numbers of any Sentry Key FOBIK transponder that is programmed into it. A maximum of eight Sentry Key FOBIK transponders can be programmed into the RFH. For added system security, each RFH 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 FOBIK that is programmed into the RFH. 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 RFH Secured Access Mode. The Secured Access Mode is required during service to perform the SKIS initialization and Sentry Key FOBIK transponder programming procedures. The RFH 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 RFH replacement is required, the Secret Key code can be transferred to the new RFH 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 FOBIK units to be programmed into the new RFH so that new FOBIK units will not be required. In the event that the original Secret Key code cannot be recovered, RFH replacement will also require new Sentry Key FOBIK units. The diagnostic scan tool will alert the technician during the SKIS initialization procedure if new Sentry Key FOBIK units are required. Refer to STANDARD PROCEDURE .
When the status of the ignition switch transitions to On, the RFH transmits a LF signal to excite the transponder in the FOBIK. The RFH then waits for a RF signal response from the transponder. If the response received identifies the FOBIK as valid, the RFH sends an electronic valid key message to the PCM over the CAN data bus. If the response received identifies the FOBIK as invalid or if no response is received from the FOBIK transponder, the RFH sends an invalid key message to the PCM. The PCM will enable or disable engine operation based upon the status of the RFH 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 RFH by the PCM, the engine will be disabled and the vehicle immobilized after two seconds of running.
The RFH 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 RFH 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 RFH 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 RFH detects a system malfunction or the SKIS has become ineffective, the security indicator will stay On solid. If the RFH detects an invalid FOBIK or if a FOBIK transponder-related fault exists, the security indicator will flash.
The RFH performs a self-test of the SKIS each time the status of the ignition transitions out of Off, and will store fault information in the form of a Diagnostic Trouble Code (DTC) if a system malfunction is detected. The RFH will also send an electronic message to the IPC if a fault is detected, and the IPC responds by illuminating the security indicator.
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, procedures for proper wire and connector repair, 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.