Sentry Key Immobilizer System
The Sentry Key Immobilizer System (SKIS) is designed to provide passive protection against unauthorized vehicle use by disabling the engine whenever an attempt is made to operate the vehicle using anything other than a key or Frequency Operated Button with Integrated Key (FOBIK) equipped with a valid 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 microcontroller-based Radio Frequency Hub (RFH) uses Radio Frequency (RF) communication to challenge and obtain confirmation that the key or FOBIK being used is a valid key or FOBIK for operating the vehicle. The microcontroller-based RFH hardware and software also uses electronic messages to communicate with the IGnition Node Module (IGNM) (without Passive Entry Keyless Go/PEKG) or Keyless Ignition Node (KIN) (with PEKG) over a private serial bus and with other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. Refer to COMMUNICATION, OPERATION .
Pre-programmed key transponders are provided with the vehicle from the factory. Each RFH will recognize a maximum of eight keys or FOBIK units. If the customer would like additional keys or FOBIK units other than those provided with the vehicle, they may be purchased from any authorized dealer. These additional keys or FOBIK units must be programmed to the RFH in the vehicle in order for the system to recognize them as valid keys. This can be done by the dealer using a diagnostic scan tool. Refer to STANDARD PROCEDURE .
In vehicles equipped with an export premium version of the Vehicle Theft Alarm (VTA), the Body Control Module (BCM) controls an electronic shaft lock module (also known as the Electronic Steering-column Lock/ESL or the Electronic Steering Column Lock/ESL) on the steering column that locks the steering shaft from rotation unless the BCM receives a electronic valid key message from the RFH. The BCM also communicates with the electronic shaft lock module over the CAN data bus to monitor and control the shaft lock function.
In vehicles with a rotary ignition switch the RFH 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 RFH. In vehicles with the push button Keyless Go (KG) system, the RFH transmits 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, while the IGNM 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 RFH.
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 and for the Tire Pressure Monitoring (TPM) system. Refer to DESCRIPTION or OPERATION . Refer to TIRE PRESSURE MONITORING, DESCRIPTION . The RFH 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 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 or FOBIK transponder that is programmed into it. A maximum of eight Sentry Key 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 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 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. The Body Control Module (BCM) stores and compares vehicle configuration data with the RFH as well as with other Electronic Control Units (ECU) in the vehicle. This process is referred to as PRogramming Of Configuration of Systems Integrated (PROCSI) (also known as PROXI). If a configuration mismatch is detected, the BCM sets a DTC. A configuration mismatch DTC will require the performance of a Restore BCM PROXI Configuration routine, or a PROXI Configuration Alignment routine using a diagnostic scan tool.
Proper completion of the SKIS initialization will allow the existing Sentry Key transponders to be programmed into the new RFH so that new Sentry Key transponders will not be required. In the event that the original Secret Key code cannot be recovered, RFH replacement will also require new Sentry Key transponders. The diagnostic scan tool will alert the technician during the SKIS initialization procedure if new Sentry Key transponders 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 LF signal response from the transponder. If the response received identifies the key or 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 key or FOBIK as invalid or if no response is received from the key or 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 key or FOBIK, or if a key or FOBIK transponder-related fault exists, the security indicator will flash.
The BCM performs a self-test of the SKIS and the shaft lock module each time the ignition status 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 BCM will illuminate the security indicator in the IPC or the IPC will display a textual SHAFT LOCK ERROR message in the Electronic Vehicle Information Center (EVIC) display 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.