Power to many of this vehicle's circuits are controlled by the module that is designated the Power Mode Master (PMM). This vehicle's PMM is the Body Control Module (BCM). The PMM controls which power mode (Run, Accessory, Crank, or Off) is active.
Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the Power Mode Master (PMM). The BCM is the PMM on this vehicle. The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Class 2 Serial Data circuit.
To determine the correct power mode the PMM uses the following circuits:
• Ignition 0
• Ignition 1
• Ignition 3
Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid PMM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, battery positive voltage, the modules will fail-safe to the RUN power mode. If the discrete ignition input is not active, open, or 0 volts, the modules will fail-safe to OFF-AWAKE. In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
Do you know what class 2 is ?
Class 2 Serial Data Link
The following modules use the class 2 serial data link to communicate with each other:
• The body control module (BCM)
• The digital radio receiver (DRR)
• The electronic brake control module (EBCM)
• The inflatable restraint sensing and diagnostic module (SDM)
• The powertrain control module (PCM)
• The radio
• The vehicle theft deterrent (VTD)
The class 2 serial data link also allows a scan tool to communicate with the above modules for diagnostic and testing purposes.
The class 2 serial data link on this vehicle is configured in a star pattern. There is no redundant path for the serial data to flow through. If a class 2 serial data circuit develops an open condition, the module connected by that circuit will not be able to communicate.
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Enter vehicle info. under system click on engine ,then under sub system click starting .