Key, Transponder: Operation

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

In vehicles that are equipped with the PEKG system and KIN, the RFH 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 RFH 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 RFH to the Powertrain Control Module (PCM) 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 RFH over the CAN data bus, the engine will be disabled after about two seconds of operation. The Instrument Panel Cluster (IPC) 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 RFH has a unique Secret Key code programmed into it by the manufacturer. When a Sentry Key is programmed into the memory of the RFH, the RFH stores the transponder identification code from the Sentry Key, and the Sentry Key learns the Secret Key code from the RFH. Once the Sentry Key learns the Secret Key code of the RFH, 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 RFH 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 IPC indicates that there is a SKIS system failure such as:

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