Antitheft and Alarm Systems: Description and Operation

SENTRY KEY IMMOBILIZER SYSTEM (SKIS)
The SKIS is an immobilizer system designed to prevent unauthorized vehicle operation. The system consists of a Sentry Key Immobilizer Module (SKIM) and ignition key(s) called Sentry Key(s) which are equipped with a transponder chip. The SKIM communicates over the Chrysler Collision Detection (CCD) data bus network to the Powertrain Control Module (PCM), instrument cluster and/or the DRB scan tool.

When the ignition is turned to the RUN/START position, the SKIM produces a Radio Frequency (RF) via an antenna which is located around the ignition lock cylinder. The RF powers up the transponder chip inside the Smart Key. The transponder chip then emits a coded signal that is received by the SKIM antenna. If this coded signal is valid, the SKIM sends a "VALID KEY" message to the PCM. If the first transponder signal is not valid, the SKIM will attempt four more times to receive a correct transponder signal. If a valid signal is not received, the SKIM stores a diagnostic trouble code and sends an "INVALID KEY" message to the PCM. Then the PCM will allow the engine to start for approximately two seconds and stall.

The SKIS includes two valid Smart Keys from the factory. If the customer wishes, additional uncoded Smart Key blanks are available. These blank keys must be cut to match a valid key, but the engine will not start unless the transponder chip inside the blank key is programmed to that particular vehicle.

The Sentry Key Immobilizer System (SKIS) can be programmed to recognize a total of eight keys. For programming the Smart Key Transponder, refer to Maintenance and Service Information.

The SKIM also sends messages to the instrument cluster over the CCD bus to control the indicator lamp. The SKIM sends a message to the instrument cluster to turn the lamp on for about three seconds when the ignition is turned to the Run/Start position as a bulb test. If the 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 an invalid key is detected in the ignition key cylinder with the ignition switch in the Run/Start position, or when the SKIM has entered its customer key programming mode, the SKIM Will flash the SKIS indicator lamp ON and OFF.

SENTRY KEY IMMOBILIZER CODES
Typically, modules have Diagnostic Trouble Codes that are referred to as either active or stored. In the case of the Sentry Key Immobilizer Module, however, all codes are stored codes. The two various types of stored codes in the SKIM can be considered to be either current or pre-existing codes. If more than one code exists, diagnostic priority should be given to the current code(s). A current code indicates a malfunction that is CURRENT at the time of vehicle service. A pre-existing code indicates the malfunction is not currently present. If a malfunction is not detected after 80 ignition cycles, the code will automatically be erased.