Alarm Module: Description and Operation
SENTRY KEY IMMOBILIZER MODULEThe Sentry Key Immobilizer Module (SKIM) contains a Radio Frequency (RF) transceiver and a central processing unit, which includes the Sentry Key Immobilizer System (SKIS) program logic. The SKIS programming enables the SKIM to program and retain in memory the codes of at least one, but no more than eight electronically coded Sentry Key transponders. The SKIS programming also enables the SKIM to communicate over the Chrysler Collision Detection (CCD) data bus network with the Powertrain Control Module (PCM), the instrument cluster and/or the DRB III scan tool.
The SKIM transmits and receives RF signals through a tuned antenna enclosed within a molded plastic ring formation that is integral to the SKIM housing. When the SKIM is properly installed on the steering column, the antenna ring is oriented around the circumference of the ignition lock cylinder housing. This antenna ring must be located within eight millimeters (0.31 inches) of the Sentry Key in order to ensure proper RF communication between the SKIM and the Sentry Key transponder.
For added system security, each SKIM is programmed with a unique "Secret Key" code and a security code (PIN). The SKIM keeps the "Secret Key" code in memory This "Secret Key" code must be transferred to the PCM memory during the initialization/programming of the SKIS when the vehicle is manufactured, and each time the PCM is replaced during vehicle service by the dealer technician. The SKIM also transfers the "Secret Key" code to the memory of each of the Sentry Key transponders during new key programming. The security code is used by the assembly plant to access the SKIS for initialization, or by the dealer technician to access the system for service. The SKIM also stores in its memory the Vehicle Identification Number (VIN), which it learns through a CCD data bus message from the PCM during initialization.
The SKIM and the PCM both use software that includes a rolling code algorithm strategy, which helps to reduce the possibility of unauthorized SKIS disarming. The rolling code algorithm ensures security by preventing an override of the SKIS through the unauthorized substitution of the SKIM or the PCM. However, the use of this strategy also means that replacement of either the SKIM or the PCM units will require a system initialization procedure to restore system operation.
When the ignition switch is turned to the ON or START positions, the SKIM transmits an RF signal to excite the Sentry Key transponder. The SKIM then listens for a return RF signal from the transponder of the Sentry Key that is inserted in the ignition lock cylinder. If the SKIM receives an RF signal with valid "Secret Key" and transponder identification codes, the SKIM sends a "valid key" message to the PCM over the CCD data bus. If the SKIM receives an invalid RF signal or no response, it sends "invalid key" messages to the PCM. The PCM will enable or disable engine operation based upon the status of the SKIM messages.
The SKIM also sends messages to the instrument cluster over the CCD data bus network to control the SKIS indicator lamp. The SKIM sends messages to the instrument cluster to turn the lamp on for about three seconds when the ignition switch is turned to the ON position as a bulb test. After completion of the bulb test, the SKIM sends bus messages to keep the lamp off for a duration of about one second. Then the SKIM sends messages to turn the lamp on or off based upon the results of the SKIS self-tests. If the SKIS indicator lamp comes on and stays on after the bulb test, it indicates that the SKIM has detected a system malfunction and/or that the SKIS has become inoperative.
If the SKIM detects an invalid key when the ignition switch is turned to the ON position, it sends messages to the instrument cluster to flash the SKIS indicator lamp. The SKIM can also send messages to the instrument cluster to flash the lamp and to generate a single audible chime tone. These functions serve as an indication to the customer that the SKIS has been placed in its "Customer Learn" programming mode. See Sentry Key Immobilizer System Transponder Programming for more information on the "Customer Learn" programming mode.
For diagnosis or initialization of the SKIM and the PCM, a DRB III scan tool and the proper Diagnostic Procedures are required. The SKIM cannot be repaired and, if faulty or damaged, the unit must be replaced.
SENTRY KEY IMMOBILIZER MODULE TROUBLE CODES
Antenna Failure
EEPROM Failure
Internal SKIM Failure
PCM Status Failure
Rolling Code Failure
Serial Link External Failure
Serial Link Internal Failure
Transponder Communication Failure
Transponder (Cyclic Redundancy Check) CRC Failure
Transponder ID Mismatched
Transponder Response Mismatch VIN Mismatch
SENTRY KEY IMMOBILIZER MODULE REPLACEMENT AND SYSTEM INITIALIZATION PROCESS
IMPORTANT NOTE: IF THE POWERTRAIN CONTROL MODULE HAS BEEN CHANGED AND THE CORRECT VIN AND MILEAGE HAVE NOT BEEN PROGRAMMED, A DTC WILL BE SET IN THE AIRBAG MODULE. IN ADDITION, IF THE VEHICLE IS EQUIPPED WITH A SENTRY KEY IMMOBILIZER MODULE (SKIM), SECRET KEY DATA MUST BE UPDATED TO ENABLE STARTING.
The Sentry Key Immobilizer Module (SKIM) Replacement and System Initialization Process can be summarized by the following:
1. Obtain the vehicle's unique PIN number assigned to its original SKIM module from either the vehicle's invoice or from Chrysler's Customer Center.
2. With the DRB, select "Theft Alarm," "Skim," "Miscellaneous." Select "SKIM Module Replaced" and the DRB will prompt you through the following steps.
3. Program the unique 4 digit PIN number into the SKIM's memory.
4. Program the vehicle's VIN number into the SKIM's memory.
5. Program the county code into the SKIM's memory (U.S.).
6. Transfer the vehicle's unique Secret Key data from the PCM. This process will require the SKIM module to be in secured access mode. The PIN number must be entered into the DRB before the SKIM will enter secured access mode. Once secured access mode is active, the SKIM will remain in that mode for 60 seconds.
7. Program all customer keys into the SKIM's memory. This requires that the SKIM be in secured access mode. The SKIM module will immediately exit secured access mode after each key is programmed. Note: Secured access mode is not required to query the programmed status of the key.
NOTE:
- IF A PCM IS REPLACED, THE UNIQUE SECRET KEY DATA MUST BE TRANSFERRED FROM THE SKIM MODULE TO THE PCM. THIS PROCEDURE REQUIRES THE SKIM TO BE PLACED IN SECURED ACCESS MODE USING THE FOUR DIGIT PIN CODE.
- IF THREE ATTEMPTS ARE MADE TO ENTER SECURED ACCESS MODE USING AN INCORRECT PIN, SECURED ACCESS MODE WILL BE LOCKED OUT FOR ONE HOUR. TO EXIT THIS LOCK OUT MODE, LEAVE THE IGNITION SWITCH IN THE RUN POSITION CONTINUOUSLY FOR ONE HOUR. (ENSURE ALL ACCESSORIES ARE TURNED OFF. ALSO MONITOR THE BATTERY STATE AND CONNECT A BATTERY CHARGER IF NECESSARY).
To program Sentry Keys using the "customer programming" method, which requires two valid Sentry Keys.