Immobilizer Description and Operation without RPO Y41

The immobilizer system functions are provided by the theft deterrent module (TDM) and the engine control module (ECM). When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the head of the key is energized by the exciter coil surrounding the ignition lock cylinder. This exciter coil is part of the TDM. The energized transponder transmits a signal that contains its unique value, which is received by the TDM. The TDM then compares this value to a value stored in memory. If the values match, the TDM will send the prerelease password via the serial data circuit to the ECM. If the transponders unique value is incorrect, the TDM will send the fuel disable password to the ECM.

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

The components of the theft system are as follows:

Vehicles with steering column mounted ignition switches have the exciter integral with the theft deterrent module (TDM), which is located within the steering column. The TDM can learn up to 10 keys (transponder values).

The TDM uses the following inputs: battery voltage, ignition switched voltage and ground circuit. The theft deterrent control module uses the following outputs: password exchange and challenge/response with the engine control module (ECM).

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

When the engine control module (ECM) receives the theft deterrent module (TDM) prerelease password, the ECM will challenge the password. The ECM sends this challenge back to the TDM via the serial data circuit. Both the ECM and TDM perform a calculation on this challenge. If the calculated response from the TDM equals the calculation performed by the ECM, the ECM will allow vehicle starting.

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

The ignition key for Passkey III+ (PK3+) equipped vehicles is a standard ignition key with a transponder located in the plastic head of the key. The transponder 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. There are approximately 3 trillion possible transponder values. There are no visible electrical contacts. The keys are identified by + symbol in a circle stamped into the steel shank of the key. The immobilizer system use the following types of ignition keys:

Master Keys

Master keys have a black plastic head for full access operation of the vehicle. Master keys may perform the following functions:

Valet Keys

Important: Valet keys are NOT standard equipment on all GM vehicle lines.

Valet keys have a gray plastic head and are for restricted operation of the vehicle. Valet keys may perform the following functions:

Fleet Keys

Important: Fleet keys are NOT standard equipment on all GM vehicle lines.

Fleets keys allow full access to the vehicle just as a master key would. However, unlike a master key which may only learn 10 keys to a particular vehicle, an unlimited number of fleet keys may be learned to the vehicle. Fleet keys are only used in vehicles configured for fleet use with RPO 6E2 or 6E8.

The theft deterrent module (TDM) can command the instrument panel cluster (IPC) to illuminate the security indicator only when the ignition key is in the ON position. The TDM will command the security indicator be illuminated any time a fault is noted in the immobilizer system and when the engine starting is disabled.

Immobilizer Description and Operation with RPO Y41

The immobilizer system is incorporated into the remote control door lock receiver (RCDLR). The immobilizer is provided in order to prevent the vehicle operation if an incorrect or unprogrammed keyless entry transmitter is used in an attempt to start the vehicle. When the brake is pressed or the ignition control knob is pushed in and rotated, the console passive antenna broadcasts a low frequency (LF) challenge to the transmitter. The transmitter will respond to the RCDLR via radio frequency (RF). If the RCDLR determines a valid transmitter has responded, vehicle starting will be allowed. This is accomplished by the RCDLR sending a fuel enable message to the engine control module (ECM).

The design of the immobilizer system is to prevent vehicle theft by disabling the engine unless the correct transmitter is present when attempting to start the vehicle. The system is similar in concept to conventional immobilizer systems which use a normal vehicle key. The components of the immobilizer system are as follows:

The igniting mode switch is located at the right side of the steering column. The ignition mode switch is used to start the vehicle engine, turn OFF the vehicle, put the vehicle in ACC mode, or put the vehicle in RUN mode.

The key capture solenoid allows the ignition control knob to be rotated through its various positions: OFF, ACCY, CRANK and RUN. The key capture solenoid is controlled by the RCDLR. Ground is applied to key capture solenoid through the park switch. If the vehicle is not in park, the solenoid will not be activated and the ignition control knob cannot be turned to the off position.

When the ignition control knob is pushed in or the brake pedal is pressed, the RCDLR looks for a valid transmitter on the interior of the vehicle. If a valid transmitter is detected, the RCDLR applies voltage to the key capture solenoid control circuit, which then allows the ignition control knob to be turned to the RUN position.

The keyless entry transmitters are not only used to passively or actively lock and unlock the vehicle, they are also used to allow vehicle starting. If the RCDLR does not receive a valid RF response after the transmitter is challenged, the RCDLR will not send a fuel enable message to the ECM. If the RCDLR is unable to establish communication with the transmitter during an attempted engine start, the ELECTRONIC KEY NOT DETECTED message will display on the driver information center (DIC).

When any one of the programmed key fobs are challenged by pushing in the control knob, it will passively send a RF signal to the RCDLR. The RCDLR will then send a serial data message to the ECM to enable engine starting.

The console keyless entry antenna is located in the center console, under the cupholder. The purpose of the console keyless entry antenna is to send a low frequency RF challenge to a programmed transmitter within the interior of the vehicle when authentication is requested (brake pedal pressed or ignition control knob is pushed in). The console keyless entry antenna is controlled by the RCDLR.

The challenge from the console antenna can reach almost all areas inside the vehicle, with the exception of the rear package shelf. If the transmitter cannot be located inside the vehicle via the console antenna, the console active antenna is used.

If the RCDLR does not receive a valid response from a programmed transmitter, it will not allow the ignition control knob to rotate, and the DIC will display the message "ELECTRONIC KEY NOT DETECTED." See Electronic Key Not Detected

The console active antenna is located in the center console. It has a small pocket next to it where the transmitter can be inserted if the transmitter battery is dead, weak, or the RF signal is being interrupted.

The purpose of the console active antenna is to detect a transmitter in the center console pocket when the transmitter cannot be detected inside the vehicle via the console antenna. It is only activated if the authentication sequence for starting has been attempted by the console passive antenna, but a transmitter has not be found. It is also used for programming transmitters. The console active antenna is controlled by the RCDLR.

If the RCDLR does not receive a valid response from a programmed transmitter, it will not allow the ignition control knob to rotate, and the DIC will display the message "ELECTRONIC KEY NOT DETECTED." See Electronic Key Not Detected

The RCDLR controls the console passive antenna and the console active antenna. The RCDLR also controls three other low frequency antennas used for passive vehicle entry, but not for immobilizer operations. The RCDLR will send an AC voltage signal and provide ground to the console active antenna when the ignition button is pressed and a transmitter is not found with the console passive antenna. This will enable the console active antenna to send out a low frequency broadcast challenge to a transmitter. The RCDLR also has an internal radio frequency (RF) antenna that receives the transmitter’s responses. The RCDLR is responsible for sending the fuel enable message to the ECM if all the requirements are met.

The security indicator appears on the instrument panel cluster (IPC). If the security indicator flashes or is illuminated continuously during vehicle operation, a malfunction exists within the immobilizer system. The security indicator is a dual purpose indicator. With the ignition OFF, the indicator it is controlled by the body control module (BCM) as a status indicator for the content theft deterrent system. With the ignition ON, it is controlled by the immobilizer system as a fault indicator.

The RCDLR will turn on the indicator when any of the following conditions exist:

The RCDLR will flash the indicator when any of the following conditions exist:

The ECM communicates with the RCDLR over the serial data line. If the RCDLR receives a valid transmitter RF response, the RCDLR allow the ignition to rotate to the RUN position and will send the fuel enable message to the ECM to enable the starting system. If the RCDLR does not receive a valid response from the transmitter, the ignition control knob will not rotate. Additionally, if the fuel enable password received by the ECM does match the stored password, vehicle starting will be disabled and the RCDLR will illuminate the security indicator.