Chevrolet Equinox Service Manual: Immobilizer Description and Operation Immobilizer

K89Immobilizer Control ModuleK9Body Control ModuleP16Instrument ClusterK20Engine Control Module

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

When an ignition key is inserted into the ignition lock cylinder and the ignitionis switched ON, the transponder in the key is energized by the immobilizer coil surroundingthe ignition lock cylinder. This immobilizer coil is part of the immobilizer controlmodule. The transponder transmits a signal that contains its unique value, which isreceived by the BCM through the immobilizer coil. The BCM then compares this valueto a value storedin memory. The BCM also monitors various control modules to determine if the storedenvironment 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 encryptedcode's unique value is incorrect or the environment identifier does not match, theBCM will send the start 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 performa calculation on this challenge. If the BCM calculated response to the challenge equalsthe calculation performed by the ECM, the ECM will allow vehicle starting.

The components of the theft system are as follows:

BCMECMImmobilizer control moduleIgnition keySecurity indicatorVarious control modules which store and report the environment identifierBody Control Module (BCM)

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

The BCM uses the following inputs:

Environment identifier exchange with various modulesEncrypted code from the vehicle key, received by the immobilizer control module

The BCM uses the following outputs:

Prerelease password communication with ECMChallenge/response with ECM

When an ignition key is inserted into the ignition lock cylinder and the ignitionis switched ON, the encrypted code in the key is energized by the immobilizer controlmodule surrounding the ignition lock cylinder. The energized transponder transmitsa signal that contains its unique value, which is received by the BCM. The BCM thencompares this value to the learned key code stored in memory. The BCM then performsone of the followingfunctions:

If the encrypted code value matches the values stored in the BCM memory, the BCM willsend the prerelease password to the ECM via serial data.If the encrypted code unique value does not match the value stored in the BCM, theBCM 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 willnot send any messages to the ECM.Engine Control Module (ECM)

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 ECMand BCM perform a calculation on this challenge. If the calculated response from theBCM equals the calculation performed by the ECM, the ECM will allow vehicle starting.

The ECM will disable vehicle starting if any of the following immobilization conditionsoccur:

The prerelease password is invalid.The start disable password is sent by the BCM.No passwords are received. There is no communication with the BCM.The BCM calculated response to the challenge does not equal the calculation performedby the ECM.Immobilizer Control Module

The immobilizer control module contains an immobilizer coil which surrounds the ignitioncylinder. The coil passively powers the transponder located in the ignition key whenthe key is in the ignition. When powered, the key transmits its unique value to theimmobilizer control module, which is then relayed to the BCM via a discrete serialdata circuit. The immobilizer control module also receives B+ and ground from theBCM.

The immobilizer control module is used to:

Learn keysTo start the vehicleIgnition Key

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

Environment Identifier

Various modules throughout the vehicle learn a specific environment identifier duringthe module programming process. The environment identifier is learned by each individualmodule and matches the environment identifier stored in the BCM. Prior to startingafter a battery disconnect, each of the modules which store a environment identifierwill compare their identifier to that of the identifier stored in the BCM. If allthe identifiersmatch, the engine starting process will continue. If the environment identifiers donot match, engine starting will be disabled.

Security Indicator

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