When the ignition switch is turned to ON, the key tested by immobilizer anti-theft system. While the key code is being read by immobilizer control module or integrated anti-theft control unit, the engine can start run with any key that will turn the lock cylinder. the key code is read and compared with key codes that have been stored in the memory of the immobilizer control module. If a valid key is detected, the immobilizer control module sends a serial data release message to the Engine Control Module (ECM). Included in the release message is an identification (ID) code which assures that neither the immobilizer control module nor the ECM have been substituted to defeat the system. If the ECM receives an invalid release message, the ECM performs the following action:

A Diagnostic Trouble Code (DTC) will stored if detect communication link failure between the ECM and immobilizer control module.

The Engine Control Module (ECM) is the control center of the fuel injection system. It constantly looks at the information from various sensors, and controls the systems that affect vehicle performance. The ECM also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the Service Vehicle Soon (SVS) Lamp, and store a Diagnostic Trouble Code (DTC) or DTCs which identify the problem areas to aid the technician in making repairs. The ECM received incorrect message identification.

The immobilizer module or the vehicle theft deterrent (VTD) module sends the fuel enable password to the engine control module (ECM) via the serial data circuit. The ECM then challenges this password. Both the ECM and immobilizer module perform a calculation on this challenge. If the calculated response from the immobilizer module 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 immobilizer module or the vehicle theft deterrent (VTD) module sends the fuel enable password to the engine control module (ECM) via the serial data circuit. The ECM then challenges this password. Both the ECM and immobilizer module perform a calculation on this challenge. If the calculated response from the immobilizer module 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 immobilizer module or the vehicle theft deterrent (VTD) module sends the fuel enable password to the engine control module (ECM) via the serial data circuit. The ECM then challenges this password. Both the ECM and immobilizer module perform a calculation on this challenge. If the calculated response from the immobilizer module 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 electronic throttle control (ETC) system uses an ignition voltage supply separate from the engine control module (ECM) supply. If the ECM detects a voltage difference between the two circuits, this diagnostic trouble code (DTC) will set.

The ECM monitors and compares the engine torque output against the maximum allowable engine torque.

If the requested torque is higher than the maximum allowable torque, the ECM applies engine torque limitation and DTC P1845.