Grand Cherokee 2WD V8-4.7L VIN J (2004)
Alarm System Transponder: Description and Operation
Sentry Key Immobilizer Transponder
TRANSPONDER KEY
Each ignition key used in the Sentry Key Immobilizer System (SKIS) has an integral transponder chip. Ignition keys with this feature can be readily
identified by a gray rubber cap molded onto the head of the key, while conventional ignition keys have a black molded rubber cap. The transponder
chip is concealed beneath the molded rubber cap, where it is molded into the head of the metal key. Each new Sentry Key has a unique transponder
identification code permanently programmed into it by the manufacturer. The Sentry Key transponder if faulty or damaged, must be replaced.
When the ignition switch is turned to the ON position, the Sentry Key Immobilizer Module (SKIM) communicates through its antenna with the Sentry
Key transponder using a Radio Frequency (RF) signal. The SKIM then waits 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 Powertrain Control Module (PCM) over the Programmable Communications Interface (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 two seconds of operation. The ElectroMechanical Instrument Cluster (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. Likewise, 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 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.
