Power Mode Master
The BCM on these vehicles acts as the power mode master (PMM). The ignition switch is a low current switch that outputs multiple discrete ignition switch signals to the PMM to determine the power mode, which is passed through the serial communication circuits to other controllers that require this information, and in this way the PMM activates the relays and other direct outputs of the PMM as need.
Serial Line Power Mode Master
The power supply to many circuits in this vehicle is controlled by this controller, which acts as the power mode master (PMM). On these vehicles, the body controller performs the PMM function (BCM). The ignition switch is a low current switch that provides multiple discrete ignition switch signals to the PMM to determine the power mode, which is communicated through the serial communication circuits to other controllers that require this information. The PMM activates the relays and other direct outputs of the PMM as needed. The PMM determines which power mode is required (OFF, AUXILIARY, RUNNING, START REQUEST), and transmits this information to other controllers via serial communication. Controllers with switchable voltage inputs may operate in default mode if the serial communication commands from the PMM do not match the information that individual controllers can receive on their connections.
The PMM receives signals from the ignition switch to determine the desired power mode for the driver. The following PMM power mode parameter table illustrates the correct state of these input parameters (chains) according to the position of the ignition switch.
PMM Power Mode Options
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Ignition switch position
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Transferred Power Mode
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Ignition Off/Run/Start (shutdown/run/start voltage circuits)
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Ignition Auxiliary/Start (auxiliary voltage circuit)
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Ignition work/start (voltage circuit "Ignition 1")
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Off, key out
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Turned off
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Key out/auxiliary
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Inactive
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Inactive
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Off, key inserted (LOCK - locked)
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Turned off
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Key inserted/disabled
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Inactive
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Inactive
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ACC
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Auxiliary
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Key inserted/ACC (auxiliary)
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Active
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Inactive
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ON
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Job
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Job
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Active
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Active
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START
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Start request
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Start (turning)
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Inactive
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Active
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BCM states awake/sleeping
body controller (BCM) can control all BCM controller functions or perform them while awake. The BCM enters sleep mode when active control or normal control of system functions has ceased and the set time has elapsed. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors these inputs while in sleep mode.
The BCM will wake up when one of the following wake-up signals is detected:
- Commands over a serial line.
- Battery connection detection.
- Signal to open any door.
- Headlights on.
- The key is in the ignition.
- Switching on the ignition.
- Switching on the parking lights.
- Remote lock operation or remote start command.
The BCM enters sleep mode when one of the following conditions is present:
- Ignition switch off, key out.
- Commands are not received on the serial line.
- There are no commands for output circuits.
- There are no delay timers in active countdown mode.
- No wake-up inputs.
If all of these conditions are met, the BCM enters a low power mode, or sleep mode.
Gateway
The BCM on this vehicle functions as a gateway, or converter. The gateway is designed to transmit serial line commands between the high speed GMLAN bus and the low speed GMLAN bus for data exchange between different controllers. The gateway communicates with each network according to the transmission protocol of each network.
One example of such a necessary communication is the communication between the motor controller (ECM), connected to a high-speed serial line, and the car's anti-theft system controller (VTD), connected to a low speed serial line. If these controllers cannot communicate, the vehicle's engine will not start.
All communication between the BCM and the scan tool is via a high speed GMLAN serial link. Fault code "Communication failure" usually installed on the wrong controllers with a communication fault.
Serial link control of auxiliary power hold mode (RAP)
The controllers receive a message about the power mode from the body controller via serial communication lines (BCM), indicating that the auxiliary power hold mode is set (RAP). The BCM monitors the ignition switch position, battery status, and passenger compartment door position to determine if RAP is required. At the same time, the controllers support the functioning of the systems controlled by them, in accordance with the requirements for operation in the RAP power mode. Components and systems active in RAP mode are also activated any time the ignition switch is moved to any position from the OFF position.
RAP mode is terminated when one of the following conditions is met:
- The BCM receives an input indicating that either passenger compartment door is open after the key has been removed from the ignition switch.
Important: The only door that turns off the radio in RAP mode is the driver's door. This is a function of the radio and will turn off after the set time has elapsed.
- The BCM's internal timer for RAP mode will expire in approximately 10 minutes.
- The BCM detects a decrease in battery capacity below a set limit.
The BCM then sends a RAP end message over the serial link.
Relay control of auxiliary power holding mode (RAP)
The BCM maintains voltage at the RAP relay at all times in all power modes except for "off-wake" And "start". This relay is also energized for approximately 10 minutes after the ignition is turned off and the key is removed, if no doors have been opened.
To Auxiliary Relay Powered Devices in Auxiliary Power Hold Mode (RAP) include sunroof, power window switches, and BTSI/Parking Interlock.
Body systems management
The various input and output circuits of the BCM are described in the respective function sections indicated on the wiring diagrams of the BCM. Systems associated with the BCM include, but are not limited to:
- Sound alarm - See section 9E, "Instrumentation / driver information system»
- Anti-theft system - See section 9T1, "Remote control system for locks and anti-theft system".
- Outdoor Lighting - See section 9B, "Lighting systems".
- Instrument cluster, display and control - See section 9E, "Instruments/driver information system»
- Interior lighting - See section 9B, "Lighting systems»
- Electric windows - See section 9P, "doors»
- Remote control functions - See section 9T1, "Remote control system for locks and anti-theft system»
- Car anti-theft system - See section 9T2, "Immobilizer system, anti-theft system»
- Wiper/Washer System Functions - See section 9D, "Wiper/Washer Systems»