Circuit Description

When the ignition switch is turned to ON, the ignition key is tested by the immobilizer anti-theft system. While the ignition key code is read by the theft deterrent control module, the engine can start to 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 theft deterrent control module. If a valid key is detected, the theft deterrent 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 theft deterrent 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:

• Disable the fuel injector circuit.
• Disable the fuel pump circuit.
• Disable the ignition coil.
• If a communication link failure between the ECM and theft deterrent control module is detected, this DTC sets.