Sentry Key Remote Entry System (SKIS) Operation

When ignition power is supplied to the SKREEM, the SKREEM performs an internal self-test. After the self-test is complete, the SKREEM energizes the antenna (this activates the transponder chip) and sends a challenge to the transponder chip. The transponder chip responds to the challenge by generating an encrypted response message.

After responding to the coded message, the transponder sends a transponder ID message to the SKREEM. The SKREEM compares the transponder ID message to the available valid key codes in SKREEM memory (8 key maximum at any one time). After validating the ignition key the SKREEM sends a CAN Bus message request to the ECM, then waits for the ECM response. If the ECM does not respond, the SKREEM will send the request again. If the ECM does not respond again, the SKREEM will stop sending the request and store a trouble code in memory. If the ECM sends a correct response to the SKREEM, the SKREEM sends a valid/invalid key message to the ECM. The ECM will allow or disallow engine operation based on this message.

Secret Key - an electronically stored value (identification number) that is unique to each SKREEM. The secret key is stored in the SKREEM, ECM and all ignition key transponders.

Challenge - a random number that is generated by the SKREEM at each ignition key cycle.

The secret key and challenge are the two variables used in the algorithm that produces the encrypted response message. The transponder uses the crypto algorithm to receive, decode and respond to the message sent by the SKREEM. After responding to the coded message, the transponder sends a transponder ID message to the SKREEM.