Antenna, Sentry Key: Operation: Operation

The Sentry Key Immobilizer Module (SKIM) control circuitry integral to the Body Control Module (BCM) includes a Radio Frequency (RF) transceiver. The SKIM circuitry transmits RF signals to, and receives RF signals from the Sentry Key transponder through the tuned Sentry Key antenna enclosed within the molded plastic antenna housing. If this antenna is not mounted properly around the ignition lock cylinder housing, communication problems between the SKIM control circuitry and the transponder may arise. These communication problems will result in Sentry Key transponder-related faults.

When the ignition switch is On, the SKIM control circuitry transmits an RF signal to the transponder in the ignition key. The SKIM then waits for an RF signal response from the transponder. If the response received identifies the key as valid, the SKIM control circuitry sends a valid key message to the Powertrain Control Module (PCM) over the Controller Area Network (CAN) data bus. If the response received identifies the key as invalid, or if no response is received from the key transponder, the SKIM sends an electronic invalid key  message to the PCM. The PCM will enable or disable engine operation based upon the status of the SKIM 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 SKIM by the PCM, the engine will be disabled and the vehicle immobilized after two seconds of running.

The SKIM 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 BCM memory if a system malfunction is detected. The Sentry Key antenna can be diagnosed, and any stored DTC can be retrieved using a diagnostic scan tool. Refer to the appropriate diagnostic information.