Sentry Key Immobilizer System (SKIS)

The Sentry Key Immobilizer System (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 Programmable Communication Interface multiplex system (PCI) bus network to the Body Control Module (BCM), Powertrain Control Module (PCM), and/or the DRB scan tool.

When the ignition is turned to the Run/Start position, the SKIM produces a Radio Frequency (RF) signal via an antenna which is located around the ignition lock cylinder. The RF powers up the transponder chip inside the Sentry 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 an "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 a "INVALID KEY" message to the PCM. Then the PCM will only allow the engine to start for two seconds then stall. This start and stall will be allowed up to six times, after which the PCM will disable the starter relay.

The SKIS includes two valid Sentry Keys from the factory. If the customer wishes, additional uncoded Sentry 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.

The SKIM sends messages to the Body Control Module (BCM) over the PCI bus to control the Vehicle Theft Security System (VTSS) indicator lamp. The SKIM sends a message to the BCM 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 VTSS indicator lamp on and off.