Sentry Key Immobilizer

WARNING: This page is about a different car, the 2004 Dodge Grand Caravan, 2004 Dodge Caravan, and 2004 Chrysler Town & Country. However, it is still accessible from the selected car via links, so may be relevant.

The Sentry Key Immobilizer System (SKIS) authenticates an electronically coded Transponder Key placed into the ignition and sends a valid/invalid key message to the Powertrain Control Module (PCM) based upon the results. The "VALID/INVALID KEY" message communication is performed using a rolling code algorithm via the Programmable Communication Interface (PCI) data bus. A "VALID KEY"message must be sent to the Powertrain Control Module (PCM) within two seconds of ignition ON to free the engine from immobilization.

The SKREEM contains a Radio Frequency (RF) transceiver and a microprocessor. The SKREEM 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 SKREEM 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 DRB III® scan tool. The SKREEM transmits and receives RF signals through a tuned antenna enclosed within a molded plastic ring formation that is integral to the SKREEM housing. When the SKREEM 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 SKREEM 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 SKREEM 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 heeded. In the event that the original "Secret Key" code can not be recovered, new ignition keys will be required. The DRB III® 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 SKREEM for service. The SKREEM 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 SKREEM access and/or disabling.