Body Control Module (BCM)

The immobilizer system is an integral part of the BCM and is controlled internally within the BCM. The BCM can learn up to 8 keys (transponder values).

The BCM uses the following inputs:

• Environment identifier exchange with various modules
• Encrypted code from the vehicle key, received by the remote control door lock receiver or immobilizer control module

The BCM uses the following outputs:

• Prerelease password communication with ECM
• Challenge/response with ECM

When the ignition mode switch is pressed, the low frequency antennas emit a challenge to the keyless entry transmitter. The transmitter receives this challenge and emits it's response as an RF message. The transmitter transmits a signal that contains its unique value, which is received by the BCM through the remote control door lock receiver. The BCM then compares this value to a value stored in memory. The BCM then performs one of the following functions:

• If the encrypted code value matches the values stored in the BCM memory, the BCM will send the prerelease password to the ECM via serial data.
• If the encrypted code unique value does not match the value stored in the BCM, the BCM will send the start disable message to the ECM via serial data.
• If the BCM is unable to measure the ignition key encrypted code value, the BCM will not send any messages to the ECM.