Orlando

Immobiliser Description and Operation

The immobiliser system functions are provided by the body control module (BCM) and the engine control module (ECM), as well as any modules which store and report the environment identifier.

When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder in the key is energised by the immobiliser coil surrounding the ignition lock cylinder. This immobiliser coil is part of the immobiliser aerial. The transponder transmits a signal that contains its unique value, which is received by the BCM through the immobiliser coil. The BCM then compares this value to a value stored in memory. The BCM also monitors various modules to determine if the stored environment identifiers match.

If both the environment identifier and the value received from the transponder match, the BCM will send the prerelease password via serial data to the ECM. If the encrypted code's unique value is incorrect or the environment identifier does not match, the BCM will send the fuel disable message to the ECM.

When the ECM receives the BCM prerelease password, the ECM will challenge the password. The ECM sends this challenge to the BCM via serial data. Both the ECM and BCM perform a calculation on this challenge. If the BCM calculated response to the challenge equals the calculation performed by the ECM, the ECM will allow vehicle starting.

The components of the theft system are as follows:

The immobiliser 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:

The BCM uses the following outputs:

When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the encrypted code in the key is energised by the immobiliser aerial surrounding the ignition lock cylinder. The energised transponder transmits a signal that contains its unique value, which is received by the BCM. The BCM then compares this value to the learned key code stored in memory. The BCM then performs one of the following functions:

When the ECM receives the BCM prerelease password, the ECM will challenge the password. The ECM sends this challenge to the BCM via the serial data circuit. Both the ECM and BCM perform a calculation on this challenge. If the calculated response from the BCM equals the calculation performed by the ECM, the ECM will allow vehicle starting.

The ECM will disable vehicle starting if any of the following immobilisation conditions occur:

The immobiliser aerial contains an immobiliser coil which surrounds the ignition cylinder. The coil passively powers the transponder located in the ignition key when the key is in the ignition. When powered, the key transmits its unique value to the immobiliser aerial, which is then relayed to the BCM via a LIN serial data circuit. The immobiliser aerial also receives B+ and ground from the BCM.

The immobiliser aerial is used to:

1. Learn keys
2. To start vehicle

Each ignition key contains a transponder with a unique encrypted value. The transponder's encrypted value is fixed and unable to be changed. The immobiliser system uses the ignition key transponder value to determine if a valid ignition key is being used to start the vehicle.

Various modules throughout the vehicle learn a specific environment identifier during the module programming process. The environment identifier is learned by each individual module and matches the environment identifier stored in the BCM. Prior to starting after a battery disconnect, each of the modules which store a environment identifier will compare their identifier to that of the identifier stored in the BCM. If all the identifiers match, the engine starting process will continue. If the environment identifiers do not match, engine starting will be disabled.

The BCM will command the instrument panel cluster to illuminate the security indicator when the ignition key is in the ON position to indicate a fault has occurred within the immobiliser system and when the engine starting is disabled.