Principles of Operation: Notes

NOTE: This vehicle is equipped with Passive Anti-Theft System (PATS) that disables the engine from cranking and starting if an unprogrammed PATS key is used or an invalid PCM ID is received. PATS is controlled by the Body Control Module (BCM). If there is a PATS concern that causes the engine to disabled, the Instrument Panel Cluster (IPC) displays "STARTING SYSTEM FAULT" in the message center. Refer to ANTI-THEFT - PASSIVE ANTI-THEFT SYSTEM (PATS) to diagnose a PATS concern.

The starter system controls the cranking of the engine. The starter motor is enabled by the starter relay when the relay is activated by the PCM . The starting system is electronically controlled by the PCM . The PCM requires the following inputs:

Ignition switch request to start the engine
Run/start relay voltage
PATS enable status from the BCM
Correct transmission PARK or NEUTRAL input from the Transmission Range (TR) sensor

Under normal operation when the ignition is turned to the START position, the BCM generates a key verification message. It sends this message to the PATS transceiver. The transceiver reads the key and sends a key verification message back to the BCM . If the message received does not match the key verified in the BCM memory, the engine is disabled and does not crank and start. Once the BCM determines the correct programmed key is in the ignition, the BCM sends the PCM a valid PATS message. When the PCM receives the message, it generates a response and sends it back to the BCM . If the response from the PCM does not match the response in the BCM memory, PATS is not enabled and the engine does not crank. If both the key verification and PCM ID pass, PATS is enabled. The PCM recognizes the correct electronically coded passive key and provides voltage and ground to the starter relay coil. The starter relay coil is energized causing the relay contacts to close providing voltage to the starter solenoid, allowing the starter motor to crank and start the engine. The PCM disengages the starter once an engine rpm threshold is reached, a set crank time is exceeded or the ignition is turned OFF. The BCM also enables the Run/start relay which sends voltage to the PCM . If the PCM does not receive this voltage the engine will not crank.

The TR sensor prevents operation of the starter motor unless the transmission is in NEUTRAL or PARK.