Transponder Key

When the ignition switch is turned to the On position, the SKIM communicates through its antenna with the sentry key transponder using RF signal. The SKIM then listens for a RF response from the transponder through the same antenna. The sentry key transponder chip is within the range of the SKIM transceiver antenna ring when it is inserted into the ignition lock cylinder. The SKIM determines whether a valid key is present in the ignition lock cylinder based upon the response from the transponder. If a valid key is detected, that fact is communicated by the SKIM to the PCM over the PCI data bus, and the PCM allows the engine to continue running. If the PCM receives an invalid key message, or receives no message from the SKIM over the PCI data bus, the engine will be disabled after about 2 seconds of operation. The EMIC will also respond to the invalid key message on the PCI data bus by flashing the SKIS indicator on and off.

Each sentry key has a unique transponder identification code permanently programmed into it by the manufacturer. The SKIM has a unique secret key code programmed into it by the manufacturer. When a sentry key is programmed into the memory of the SKIM, the SKIM stores the transponder identification code from the sentry key, and the sentry key learns the secret key learns the secret key code from the SKIM. Once the sentry key learns the secret key code of the SKIM, it is permanently stored in the memory of the transponder. Therefore, once a sentry key has been programmed to a particular vehicle, it cannot be used on any other vehicle. The SKIS performs a self-test each time the ignition switch is turned to the ON position, and will store key related fault information in the form of DTC's in SKIM memory if a sentry key transponder problem is detected. The sentry key transponder chip can be diagnosed, and any stored DTC's can be retrieved using a scan tool.