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Old 06-25-2014, 11:15 AM   #1
Ernest T
 
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Exactly How Does a Key Work

I see talk about key coding. How does the Camaro key work exactly?
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Old 06-25-2014, 07:16 PM   #2
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Everything you ever wanted to know about your ignition key and then some...
From GM service manual:

Immobilizer Description and Operation
The immobilizer 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 energized by the immobilizer coil surrounding the ignition lock cylinder. This immobilizer coil is part of the immobilizer antenna. The transponder transmits a signal that contains its unique value, which is received by the BCM through the immobilizer 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:

•BCM
•ECM
•Immobilizer antenna
•Ignition key
•Security indicator
•Various modules which store and report the environment identifier
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 immobilizer antenna
The BCM uses the following outputs:

•Prerelease password communication with ECM
•Challenge/response with ECM
When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the encrypted code in the key is energized by the immobilizer antenna surrounding the ignition lock cylinder. The energized 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:

•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.
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 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 immobilization conditions occur:

•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 performed by the ECM.
Immobilizer Antenna
The immobilizer antenna contains an immobilizer 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 immobilizer antenna, which is then relayed to the BCM via a LIN serial data circuit. The immobilizer antenna also receives B+ and ground from the BCM.

The immobilizer antenna is used to:

 1. Learn keys
 2. To start vehicle
Ignition Key
Each ignition key contains a transponder with a unique encrypted value. The transponder's encrypted value is fixed and unable to be changed. The immobilizer system uses the ignition key transponder value to determine if a valid ignition key is being used to start the vehicle.

Environment Identifier
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.

Security Indicator
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 immobilizer system and when the engine starting is disabled.
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Old 06-25-2014, 08:05 PM   #3
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So the fob is not needed to drive the car if I'm reading that right?
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Old 06-25-2014, 08:14 PM   #4
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Quote:
Originally Posted by Ernest T View Post
So the fob is not needed to drive the car if I'm reading that right?
With the switch blade the coding was built in the fob and was needed to start the car. Now with the separate key you will not need the fob if you do not want the remote to unlock and unlock the doors.
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Old 06-25-2014, 08:34 PM   #5
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Quote:
Originally Posted by Ernest T View Post
So the fob is not needed to drive the car if I'm reading that right?
Quote:
Originally Posted by Caddyroger View Post
With the switch blade the coding was built in the fob and was needed to start the car. Now with the separate key you will not need the fob if you do not want the remote to unlock and unlock the doors.
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Old 06-25-2014, 11:55 PM   #6
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I know he asked how, but damn dude overkill on the info
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Old 06-26-2014, 08:10 AM   #7
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I know he asked how, but damn dude overkill on the info
Overkill is my middle name
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Old 06-26-2014, 09:34 AM   #8
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Good question, good answer... thanks
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Old 06-26-2014, 09:45 AM   #9
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Remember to check your cars alarm settings to make sure it is not on auto set. If it is you will need the fob to unlock the car, using the key only could cause the alarm to go off.
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Old 11-09-2016, 01:20 PM   #10
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great answer. I need to program the transponder portion of my fob. Other than paying $65 at the dealership is there a way to do this?
I tried using the old key, starting the car up, and then switching to the new one, and no luck.

thanks
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