Circuit Description
The engine control module (ECM), the powertrain interface module (PIM) and the body control module (BCM) are integral
part of the vehicle theft deterrent system. The theft deterrent system authenticates the security code programmed into
each of these modules to prevent unauthorised vehicle operation. This authentication process includes the following
steps:
1 At predetermined conditions, the BCM sends a security code to the PIM.
2 When the ignition is switched on, the PIM receives and compares this security code from the BCM against the
security code programmed into the PIM.
3 Once the PIM receives the correct security code from the BCM, it sends a security code to the ECM.
4 The ECM receives and compares this security code from the PIM against the security code programmed into the
ECM.
5 The authentication process is complete once the ECM receives the correct security code from the PIM within the
specified time frame.
6 The ECM allows normal vehicle operation.
NOTE
If any of these authentication processes fail, the
vehicle will not start and DTCs will set. For further
information on the theft deterrent system, refer to
Section 12J Body Control Module.
To aid diagnosis, refer to 2 Wiring Diagrams and Connector Charts for the system wiring diagram and connector charts.
System Operation
The theft deterrent system uses a remote coded key to arm and disarm the system. The remote coded key is also used
to electrically lock or unlock all doors and the rear compartment lid (sedan and wagon) or rear glass liftgate (AWD
wagon).
V6 and GEN IV V8 Engine
When the ignition is turned on, the BCM sends the PIM an encrypted BCM / Key security code. The security code is
received via the slip ring, or the by remote receiver in the event of no slip ring communication. The powertrain interface
module (PIM) sends this encrypted security code to the engine control module (ECM). The ECM compares the received
security code with its own security code, and if valid, the ECM returns an OK to Start message to the BCM via the PIM. If
the BCM does not receive an OK to Start message from the ECM via the PIM within 0.5 second of the ignition ON signal,
the BCM isolates the secondary data bus and a DTC will be set. Refer to 5.8 Diagnostic Trouble Code List.
Isolation of the secondary/tertiary data bus eliminates the possibility of a device failure, other than the BCM and the PIM,
causing a problem on the bus and inhibiting theft deterrent communications. This continues until the ECM responds with
an acknowledgment or for a maximum of 5 seconds, after which the BCM switches to the standard polling sequence.
Following successful anti-theft communications, the BCM begins sequential polling of devices on the bus and normal
system operation is established.
When the ignition is off, the BCM continues to poll, allowing for Tech 2 communications and external control of the bus
prior to the ignition being switched on.