Anti-Theft Systems: Operation

When ignition switch is turned to ON or START position, Sentry Key Immobilizer Module (SKIM) sends a signal to key transponder. SKIM then receives a signal back from key when it is inserted into the ignition switch. This signal is sent to Powertrain Control Module (PCM). If signal is correct, vehicle is allowed to be started. If signal is incorrect, SKIM will send an invalid key signal to PCM. PCM will enable or disable the engine starting process depending on signal received.

SKIM also sends signal to instrument cluster to control indicator lamp. When ignition switch is turned to ON position, SKIM will turn on warning indicator for about 3 seconds as a bulb circuit check. It then turns out warning indicator for about one second. A self-test is then performed by Sentry Key Immobilizer System (SKIS), and if a problem is detected, warning indicator is turned on again, indicating a system problem, or that system is inoperative. If an invalid key is detected, warning indicator will flash, and engine cannot be started.

Sentry key transponder has a unique identification code programmed into it at factory. Transponder is within range of SKIM antenna ring when it is inserted into ignition switch. SKIM compares transponder signal to code stored in memory and determines whether key is valid or not. Additional keys can be programmed for use. Key transponder cannot be repaired and must be replaced if faulty.