Description & Operation
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 in.) 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 that controls the VTSS indicator LED. The SKIM sends messages to the Instrument Cluster 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 in this section for more information on the Customer Learn programming mode.
Removal & Installation
- Open hood.
- Disconnect and isolate the battery negative cable.
- Remove the steering column upper and lower shrouds.
- Disconnect the steering column wire harness connector from the SKIM.
- Remove the two screws securing the SKIM module to the top of the steering column.
- Rotate the SKIM and its mounting bracket upwards and then to the side away from the steering column to slide the SKIM antenna ring from around the ignition switch lock cylinder housing.
- Remove the SKIM from the vehicle.
- Rotate the SKIM and its mounting bracket to the side towards the steering column to slide the SKIM antenna ring around the ignition switch lock cylinder housing and then downwards.
- Install the two screws securing the SKIM module to the top of the steering column.
- Connect the steering column wire harness connector to the SKIM.
- Install the steering column upper and lower shrouds.
- Connect the battery negative cable.
Verify vehicle and system operation.