Jeep Liberty KJ. Manual - part 302
TRANSPONDER KEY
DESCRIPTION
Each ignition key (2) used in the Sentry Key Immobi-
lizer System (SKIS) has an integral transponder chip
included on the circuit board (4) beneath the cover (1)
of the integral Remote Keyless Entry (RKE) transmit-
ter (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 identifica-
tion code that is permanently programmed into it by
the manufacturer, and which must be programmed
into the Sentry Key REmote Entry Module (SKREEM)
to be recognized by the SKIS as a valid key.
The Sentry Key transponder cannot be adjusted or repaired. If inoperative or damaged, the entire key and RKE
transmitter unit must be replaced.
OPERATION
When the ignition switch is turned to the ON position, the Sentry Key REmote Entry Module (SKREEM) communi-
cates through its antenna with the Sentry Key transponder using a Radio Frequency (RF) signal. The SKREEM 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 transceiver antenna ring when it is inserted into the ignition lock cylinder. The
SKREEM 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 to the Powertrain Control Module
(PCM) over the Programmable Communications Interface (PCI) data bus, and the PCM allows the engine to con-
tinue running. If the PCM receives an invalid key message, or receives no message from the SKREEM over the PCI
data bus, the engine will be disabled after about two seconds of operation. The Body Control Module (BCM) will
also respond to the invalid key message on the PCI data bus by flashing the security indicator in the ElectroMe-
chanical Instrument Cluster (EMIC) on and off.
Each Sentry Key has a unique transponder identification code permanently programmed into it by the manufacturer.
Likewise, the SKREEM has a unique Secret Key code programmed into it by the manufacturer. When a Sentry Key
is programmed into the memory of the SKREEM, the SKREEM stores the transponder identification code from the
Sentry Key, and the Sentry Key learns the Secret Key code from the SKREEM. Once the Sentry Key learns the
Secret Key code of the SKREEM, 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. (Refer to 8 -
ELECTRICAL/VEHICLE THEFT SECURITY - STANDARD PROCEDURE - TRANSPONDER PROGRAMMING).
The Sentry Key Immobilizer System (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 a Diagnostic Trouble Code (DTC) in SKREEM
memory if a Sentry Key transponder problem is detected. The Sentry Key transponder chip can be diagnosed, and
any stored DTC can be retrieved using a diagnostic scan tool. Refer to the appropriate diagnostic information.
8Q - 84
VEHICLE THEFT SECURITY - SERVICE INFORMATION
KJ