Key, Transponder: Operation

When the status of the ignition switch transitions to On, the IGnition Node Module (IGNM) or the Keyless Ignition Node (KIN) (with Passive Entry Keyless Go/PEKG) sends an electronic ignition switch status  message over a private serial bus to the Radio Frequency Hub Module (RFHM). In vehicles not equipped with the PEKG system, the IGNM uses an internal antenna to communicate with the key transponder based upon inputs received from the RFHM through the private serial bus. In vehicles that are equipped with the PEKG system and KIN, the RFHM relies upon several Low Frequency (LF) antenna units to challenge the key transponders using a LF signal, then monitors responses from the 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, it is communicated by the RFHM to the Body Control Module (BCM), and by the BCM 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 BCM receives an electronic invalid key  message or no message, or if the PCM receives an electronic invalid key  message or no message over the CAN data bus, the engine will be disabled. 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 key transponder has a unique 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 key transponder is programmed into the memory of the RFHM, the RFHM stores the transponder identification code from the key transponder and the key transponder learns the Secret Key code from the RFHM. Once the key transponder learns the Secret Key code of the RFHM, it is permanently stored in the memory of the transponder. Therefore, once a key transponder 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 key transponder problem is detected. The 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:

• Two transponder keys too close to each other.
• Another transponder device (i.e.: Speed Pass) too close to the key transponder.

A security indicator illuminated solid (not flashing) in the IPC indicates that there is a system failure.

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