Sentry Key Immobilizer Module: Description

The Sentry Key Immobilizer Module (SKIM) contains a Radio Frequency (RF) transceiver and a microprocessor. The SKIM retains in memory the ID numbers of any Sentry Key that is programmed to it. The maximum number of keys that may be programmed to each module is eight (8). The SKIM also communicates over the Programmable Communication Interface (PCI) data bus with the Powertrain Control Module (PCM), the Body Control Module (BCM), the Mechanical Instrument Cluster (MIC), and the DRBIII® 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 fits snugly around the circumference of the ignition lock cylinder housing. If this ring is not mounted properly, communication problems may arise in the form of transponder-related faults.

For added system security, each SKIM is programmed with a unique "Secret Key" code. This code is stored in memory and is sent over the PCI bus to the PCM and to each key that is programmed to work with the vehicle. The "Secret Key" code is therefore a common element found in all components of the Sentry Key Immobilizer System (SKIS). In the event that a SKIM replacement is required, the "Secret Key" code can be restored from the PCM by following the SKIM replacement procedure found in the DRBIII® scan tool. Proper completion of this task will allow the existing ignition keys to be reprogrammed. Therefore, new keys will NOT be needed. In the event that the original "Secret Key" code can not be recovered, new ignition keys will be required. The DRBIII® scan tool will alert the technician if key replacement is necessary. Another security code, called a PIN, is used to gain secured access to the SKIM for service. The SKIM also stores in its memory the Vehicle Identification Number (VIN), which it learns through a bus message from the assembly plant tester. The SKIS scrambles the information that is communicated between its components in order to reduce the possibility of unauthorized SKIM access and/or disabling.