Key, Transponder: Operation: Operation

When the status of the ignition switch (also known as the Keyless Ignition Node/KIN) transitions to On, it sends an electronic ignition switch status  message over a dedicated Local Interface Network (LIN) serial bus circuit to the Radio Frequency Hub Module (RFHM) (also known as the RF Hub). In vehicles that are equipped with the PEKG system, the RFHM relies upon several Low Frequency (LF) antenna units to challenge the Sentry Key transponders using a LF signal, then monitors responses from the Sentry Key transponders received as Very High Frequency (VHF) signals. The RFHM determines whether a valid key is present based upon the response from the transponder.

If a valid key is detected, that fact is communicated by the RFHM to the Powertrain Control Module (PCM) (also known as the Engine Control Module/ECM) over the Controller Area Network (CAN) data bus, and the PCM allows the engine to continue running. If the PCM receives an invalid key message, or receives no message from the RFHM over the CAN data bus, the engine will be disabled after about two seconds of operation. The Instrument Cluster (IC) (also known as the Common Instrument Cluster/CIC) will also respond to the invalid key message on the CAN data bus by flashing the security indicator On and Off.

Likewise, when any one of the Remote Keyless Entry (RKE) transmitter buttons of the FOB with Integrated Key (FOBIK) is depressed, the on-board transmitter of the FOBIK generates a high frequency RF request signal that is received and validated by the RFHM. If the RFHM determines that the RKE transmitter RF request signal was generated by a FOBIK that is valid for the vehicle, the RFHM relays electronic request messages to the appropriate electronic modules in the vehicle over the CAN data bus to invoke the functions or features associated with the request.

Each vehicle owner is provided with a four-digit Personal Identification Number (PIN) by the dealer at the time of vehicle purchase. This number also appears on the original vehicle invoice and is required along with a diagnostic scan tool for the dealer to program an additional or replacement FOBIK into the electronics of the vehicle. The mechanical emergency key included with a new additional or replacement blank FOBIK must also be cut to match the coding of the lock cylinders in the vehicle.

Each Sentry Key has a unique transponder identification code permanently programmed into it by the manufacturer. Likewise, the RFHM has a unique Secret Key code programmed into it by the manufacturer. When a Sentry Key is programmed into the memory of the RFHM, the RFHM stores the transponder identification code from the Sentry Key, and the Sentry Key learns the Secret Key code from the RFHM. Once the Sentry Key learns the Secret Key code of the RFHM, it is permanently stored in the memory of the transponder. Therefore, once a Sentry Key has been programmed to a particular vehicle, it cannot be used on any other vehicle. Refer to STANDARD PROCEDURE .

The Sentry Key Immobilizer System (SKIS) performs a self-test each time the ignition switch status transitions to On, and will store key-related fault information in the form of a Diagnostic Trouble Code (DTC) in RFHM memory if a Sentry Key transponder problem is detected. The Sentry Key transponder chip can be diagnosed, and any stored DTC can be retrieved using a diagnostic scan tool. Refer to the appropriate diagnostic information.

Common communication problems include:

• Two transponder keys too close to each other.
• Another transponder device (i.e.: Speed Pass) too close to the Sentry Key transponder.
• Transponder too close to a cellular phone.
• A cellular phone charger in the vehicle causing interference.

A security indicator illuminated solid (not flashing) in the IC indicates that there is a SKIS system failure such as:

• Loss of PCM/CAN data bus communication.
• Failed antenna circuit.