Sentry Key Immobilizer
The Sentry Key Immobilizer System (SKIS) authenticates an electronically coded Transponder Key placed into the ignition and sends a valid/invalid key message to the Engine Control Module (ECM) based upon the results. The "VALID/INVALID KEY" message communication is performed using a rolling code algorithm. A "VALID KEY" message must be sent to the ECM within two seconds of ignition ON to free the engine from immobilization. This Controller Area Network (CAN) data bus message is sent to the ECM after first going through the SKREEM. The SKREEM is located behind the instrument cluster and has a separately mounted antenna ring mounted around the ignition cylinder which picks up the transponder key signal. See Fig 1.