Keyless Entry Module: Description and Operation
The functions and features of the Sentry Key Immobilizer Module (SKIM) (also known as the Sentry Key REmote Entry Module/SKREEM or the
Wireless Control Module/WCM) are all integral to the Wireless Ignition Node (WIN) in this vehicle. The WIN contains a Radio Frequency (RF)
transceiver and a microprocessor. The WIN transmits Low Frequency (LF) signals to, and receives LF signals from the Sentry Key transponder integral
to the FOB with Integrated Key (FOBIK) through a tuned antenna internal to the WIN housing.
The WIN also serves as the Remote Keyless Entry (RKE) RF receiver and, if the vehicle is so equipped, the receiver for the Tire Pressure Monitoring
(TPM) system. See: Body and Frame/Locks/Power Locks/Description and Operation/Description or See: Instrument Panel, Gauges and Warning
Indicators/Tire Monitoring System/Description and Operation/Tire Pressure Monitoring (TPM) - Description. The WIN communicates over the
Controller Area Network (CAN) data bus with the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), the
Powertrain Control Module (PCM) or the diagnostic scan tool. On vehicles equipped with an export premium version of the Sentry Key Immobilizer
System (SKIS), the WIN also serves as a translator module and has bi-directional communication with the shaft lock module over a dedicated Local
Interface Network (LIN) data bus.
The WIN and the PCM both use software that includes a rolling code algorithm strategy, which helps to reduce the possibility of unauthorized Sentry
Key Immobilizer System (SKIS) disarming. The rolling code algorithm ensures security by preventing an override of the SKIS through the unauthorized
substitution of the WIN or the PCM. However, the use of this strategy also means that replacement of either the WIN or the PCM units will require a
system initialization procedure to restore system operation.
The WIN retains in memory the ID numbers of any Sentry Key FOBIK transponder that is programmed into it. A maximum of eight Sentry Key FOBIK
transponders can be programmed into the WIN. For added system security, each WIN is programmed with a unique Secret Key code. This code is stored
in memory, sent over the CAN data bus to the PCM, and is encoded to the transponder of every Sentry Key FOBIK that is programmed into the WIN.
Therefore, the Secret Key code is a common element that is found in every component of the SKIS.
Another security code, called a PIN, is used to gain access to the WIN Secured Access Mode. The Secured Access Mode is required during service to
perform the SKIS initialization and Sentry Key FOBIK transponder programming procedures. The WIN also stores the Vehicle Identification Number
(VIN) in its memory, which it learns through a CAN data bus message from the PCM during SKIS initialization.
In the event that a WIN replacement is required, the Secret Key code can be transferred to the new WIN from the PCM using the diagnostic scan tool
and the SKIS initialization procedure. Proper completion of the SKIS initialization will allow the existing Sentry Key FOBIKs to be programmed into
the new WIN so that new FOBIKs will not be required. In the event that the original Secret Key code cannot be recovered, WIN replacement will also
require new Sentry Key FOBIKs. The diagnostic scan tool will alert the technician during the SKIS initialization procedure if new Sentry Key FOBIKs
When the ignition switch is turned to the ON position, the WIN transmits a LF signal to excite the transponder in the FOBIK. The WIN then waits for a
LF signal response from the transponder. If the response received identifies the FOBIK as valid, the WIN sends an electronic valid key message to the
PCM over the CAN data bus. If the response received identifies the FOBIK as invalid or if no response is received from the FOBIK transponder, the
WIN sends an invalid key message to the PCM. The PCM will enable or disable engine operation based upon the status of the WIN 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 WIN by the PCM, the engine will
be disabled and the vehicle immobilized after two seconds of running.
The WIN also sends electronic security indicator request messages to the EMIC over the CAN data bus to tell the EMIC how to operate the security
indicator. The security indicator request message from the WIN tells the EMIC to turn the indicator ON for about three seconds each time the ignition
switch is turned to the ON position as a bulb test. After completion of the bulb test, the WIN sends security indicator request messages to the EMIC to
turn the indicator OFF, turn the indicator ON, or to flash the indicator ON and OFF. If the security indicator flashes or stays ON solid after the bulb test,
it signifies a SKIS fault. If the WIN detects a system malfunction or the SKIS has become ineffective, the security indicator will stay ON solid. If the
WIN detects an invalid FOBIK or if a FOBIK transponder-related fault exists, the security indicator will flash. If the vehicle is equipped with the
Customer Learn transponder programming feature, the WIN will also send messages to the EMIC to flash the security indicator whenever the Customer
Learn programming mode is being utilized. .
The SKIS 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 WIN memory if a system malfunction is detected. The hard wired circuits of the WIN may be diagnosed using conventional
diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the
diagnosis of the WIN or the electronic controls or communication between other modules and devices that provide some features of the SKIS. The most
reliable, efficient, and accurate means to diagnose the WIN or the electronic controls and communication related to WIN operation requires the use of a
diagnostic scan tool. Refer to the appropriate diagnostic information.