Alarm System Transponder: Description and Operation
Each ignition key (2) used in the Sentry Key Remote Entry System (SKREES), sometimes referred to as the Sentry Key Immobilizer System (SKIS) has
a transponder chip included on the circuit board (4) beneath the cover (1) of the integral Remote Keyless Entry (RKE) transmitter (3). In addition to
having to be cut to match the mechanical coding of the ignition lock cylinder and programmed for operation of the RKE system, each new Sentry Key
has a unique transponder identification code that is permanently programmed into it by the manufacturer, and which must be programmed into the Sentry
Key REmote Entry Module (SKREEM), sometimes referred to as the Wireless Control Module (WCM), to be recognized by the SKREES/SKIS as a
The Sentry Key transponder cannot be adjusted or repaired. If faulty or damaged, the entire key and RKE transmitter unit must be replaced.
When the ignition switch is turned to the On position, the Sentry Key Remote Entry Module (SKREEM), sometimes referred to as the Wireless Control
Module (WCM), communicates through its antenna with the Sentry Key transponder using a Radio Frequency (RF) signal. The SKREEM/WCM then
listens for a RF response from the transponder through the same antenna. The Sentry Key transponder chip is within the range of the SKREEM/WCM
transceiver antenna ring when it is inserted into the ignition lock cylinder. The SKREEM/WCM 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 SKREEM/WCM to the
Powertrain Control Module (PCM) over the Controller Area Network (CAN) 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 SKREEM/WCM over the CAN 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 CAN data bus by flashing
the security indicator on and off.
Each Sentry Key has a unique transponder identification code permanently programmed into it by the manufacturer. Likewise, the SKREEM/WCM has a
unique Secret Key code programmed into it by the manufacturer. When a Sentry Key is programmed into the memory of the SKREEM/WCM, the
SKREEM/WCM stores the transponder identification code from the Sentry Key, and the Sentry Key learns the Secret Key code from the
SKREEM/WCM. Once the Sentry Key learns the Secret Key code of the SKREEM/WCM, 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 Sentry Key REmote Entry System (SKREES), sometimes referred to as the Sentry Key Immobilizer System (SKIS), performs a self-test each time