Transponder Key - Operation

OPERATION

When the status of the ignition switch transitions to ON the Keyless Ignition Node (KIN) (also known as the Ignition Node Module/IGNM) sends an electronic ignition switch status message over a private serial bus to the Radio Frequency Hub Module (RFHM) (also known as the RF Hub). In vehicles not equipped with the Passive Entry Keyless Go (PEKG) system, the KIN uses an internal antenna to communicate with the Sentry Key transponder based upon inputs received from the RFHM through the private serial bus.

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.

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 .

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.

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.

NOTE:
After a RFHM is replaced with a new unit, the Sentry Key transponders need to be programmed to the new RFHM. Follow the instructions found in the diagnostic scan tool for the Replace RFHM Routine. The Sentry Key transponders and the Remote Keyless Entry (RKE) transmitters (if equipped) will both be programmed during this operation. There is no need to program the RKE transmitter again once the Sentry Key transponder key has been programmed to the new RFHM.

NOTE:
When a PCM and the RFHM are replaced at the same time, perform the following steps in order:
- Program the new PCM.

- Program the new RFHM.
Program all Sentry Key transponders to the new RFHM.