Sentry Key Immobilizer System

Sentry Key Immobilizer System (SKIS) is designed to prevent unauthorized vehicle operation. SKIS components include Sentry Key Immobilizer Module (SKIM), sentry keys and Powertrain Control Module (PCM). Sentry keys communicate with SKIM with an internal transponder chip located in plastic of sentry key. When ignition switch is turned on, SKIM sends a "challenge" signal to transponder in sentry key. Sentry key will respond to the "challenge" by responding to SKIM with encrypted secret key data. If secret key data matches stored data in SKIM, SKIM will send a signal along PCI bus to PCM to allow engine to continue to operate. If secret key data does not match stored data in SKIM, to zero-out fuel injector pulse-width and engine will not be allowed to run continuously. Vehicle will start next time a valid ignition key is used.

SKIS uses a warning light located in instrument cluster. Warning light is illuminated when SKIM sends a PCI bus message to instrument cluster for bulb check with ignition switch in RUN position, and to alert operator of a SKIS malfunction. SKIS warning light remains illuminated for all faults except transponder faults and Vehicle Identification Number (VIN) mismatch. If transponder fault is present, SKIS warning light flashes at a rate of once per second. If another fault is present, SKIS warning light will remain illuminated or flashing for duration of complete ignition cycle.

If a fault is stored in SKIM memory which prevents system from operating properly, PCM will allow engine to start and run momentarily (for a duration of 2 seconds) up to 6 times. After sixth attempt, PCM disables starter relay until fault is corrected. Large metallic objects or items such as gas station speed pay devices on key chain may cause vehicle starting problems. SKIS cannot be damaged by these devices, but intermittent no-start conditions may arise. If a problem occurs, remove items from key chain and attempt to start vehicle again.