Sentry Key Immobilizer Module (SKREEM) - Operation

OPERATION

The Sentry Key REmote Entry Module (SKREEM), sometimes referred to as the Wireless Control Module (WCM), contains a Radio Frequency (RF) transceiver and a microprocessor. The SKREEM/WCM transmits RF signals to, and receives RF signals from the Sentry Key transponder through a tuned antenna enclosed within the molded plastic antenna ring integral to the SKREEM/WCM housing. If this antenna ring is not mounted properly around the ignition lock cylinder housing, communication problems between the SKREEM/WCM and the transponder may arise. These communication problems will result in Sentry Key transponder-related faults.

The SKREEM also serves as the Remote Keyless Entry (RKE) RF receiver and, if the vehicle is so equipped, the receiver for the Tire Pressure Monitoring (TPM) system. Power Locks - Description or Tire Pressure Monitoring (TPM) - Description. The SKREEM/WCM communicates over the Controller Area Network (CAN) data bus with the ElectroMechanical Instrument Cluster (EMIC) (sometimes referred to as the Cab Compartment Node (CCN), the Powertrain Control Module (PCM), and/or the diagnostic scan tool.

The SKREEM/WCM retains in memory the ID numbers of any Sentry Key transponder that is programmed into it. A maximum of eight Sentry Key transponders can be programmed into the SKREEM/WCM. For added system security, each SKREEM/WCM 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 SKREEM/WCM. Therefore, the Secret Key code is a common element that is found in every component of the Sentry Key Immobilizer System (SKIS). Another security code, called a PIN, is used to gain access to the SKREEM/WCM Secured Access Mode. The Secured Access Mode is required during service to perform the SKIS initialization and Sentry Key transponder programming procedures. The SKREEM/WCM 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.

NOTE: After a SKREEM/WCM is replaced, the ignition/transponder keys need to be programmed to the new SKREEM/WCM. Follow the directions on the diagnostic scan tool. The transponder key for the SKREEM/SKIM and the RKE will both be programmed during this operation. There is no need to program the fob of the key for RKE functionality once the transponder key is programmed to the new SKREEM/WCM.

In the event that a SKREEM/WCM replacement is required, the Secret Key code can be transferred to the new SKREEM/WCM from the PCM using the diagnostic scan tool and the SKIS initialization procedure. Proper completion of the SKIS initialization will allow the existing Sentry Keys to be programmed into the new SKREEM/WCM so that new keys will not be required. In the event that the original Secret Key code cannot be recovered, SKREEM/WCM replacement will also require new Sentry Keys. The diagnostic scan tool will alert the technician during the SKIS initialization procedure if new Sentry Keys are required.

When the ignition switch is turned to the On position, the SKREEM/WCM transmits an RF signal to the transponder in the ignition key. The SKREEM/WCM then waits for an RF signal response from the transponder. If the response received identifies the key as valid, the SKREEM/WCM sends a valid key message to the PCM over the CAN data bus. If the response received identifies the key as invalid or if no response is received from the key transponder, the SKREEM/WCM sends an invalid key message to the PCM. The PCM will enable or disable engine operation based upon the status of the SKREEM/WCM 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 SKREEM/WCM by the PCM, the engine will be disabled and the vehicle immobilized after two seconds of running.

The SKREEM/WCM also sends security indicator status messages to the EMIC/CCN over the CAN data bus to tell the EMIC/CCN how to operate the security indicator. The security indicator status message from the SKREEM/WCM tells the EMIC/CCN to turn the indicator on for about three seconds each time the ignition switch is turned to the On position as a bulb test. After completion of the bulb test, the SKREEM/WCM sends security indicator status messages to the EMIC/CCN 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 SKREEM/WCM detects a system malfunction and/or the SKIS has become inoperative, the security indicator will stay on solid. If the SKREEM/WCM detects an invalid key or if a key transponder-related fault exists, the security indicator will flash. If the vehicle is equipped with the Customer Learn transponder programming feature, the SKREEM/WCM will also send messages to the EMIC/CCN to flash the security indicator whenever the Customer Learn programming mode is being utilized Testing and Inspection.

The SKIS performs a self-test each time the ignition switch is turned to the On position, and will store fault information in the form of a Diagnostic Trouble Code (DTC) in SKREEM/WCM memory if a system malfunction is detected. The SKREEM/WCM can be diagnosed, and any stored DTC can be retrieved using a diagnostic scan tool. Refer to the appropriate diagnostic information.