Wake-Up State
The BCM performs the BCM functions in the wake-up state. The BCM enters the sleep state when the active control or monitoring of system malfunctions has stopped, or when the BCM is idling. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors the BCM inputs during the sleep state, allowing the BCM to switch between the 2 states. The BCM wake-ups are as follows:
| • | Door ajar switches |
| • | Door handle switches |
| • | Dome lamp |
| • | Park lamps |
| • | Power door lock switches |
| • | Interior lamp request active |
| • | Ignition key put into the ignition switch |
| • | Ignition key removed from the ignition switch |
| • | Ignition in the RUN position |
| • | Key in door lock switch |
| • | RFA request to the BCM |
| • | Any Class 2 communication requiring BCM interaction |
Asleep States
The BCM is asleep when the BCM has stopped controlling or monitoring devices and has become idle again. After the ignition switch is turned to the LOCK position and 20 minutes (1216 seconds) elapse without any Wake-Up signals, the BCM enters into an asleep state and goes into the low power mode. If the BCM is in low power mode and detects a wake up, the BCM will enter into the wake-up state and enter the high power mode. If the vehicle has been left inactive (ignition in the LOCK position and no BCM wake-ups) for 20 minutes, the BCM will return to the low power mode.
BCM Controlled/Aided Functions
The BCM controls/aids the following functions. For additional circuit information and descriptions, refer to the appropriate sub-system.
| • | RKE Remote Keyless Entry/Panic Alarm/LOCKING and UNLOCKING of Doors/Lockout Prevention |
| • | DRL Daytime Running Lamps/Auto Headlamps/Exterior Lighting |
| • | VTD Vehicle Theft Deterrent/Passlock™ System |
| • | Inadvertent Power Relay/Battery Rundown Protection |
| • | RAP Retained Accessory Power |
| • | Interior Lighting |
| • | Audible Warnings |
Detailed descriptions of functions reside within the respective sub-subsystem circuit description and operation.
Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the Body Control Module (BCM). The BCM receives 2 signals/circuits from the ignition switch. These are the Ignition 1 and Ignition 3 signals/circuits.
To determine the correct power mode the BCM uses:
| • | The state of these signals/circuits, either switch closed (B+ = 1) or switch open (open = 0) |
| • | The status of the engine run flag. |
The chart indicates the modes detected and transmitted by the BCM:
Ignition Key Position | Power Mode Parameter | Engine Run Flag Serial Data | Sampled Ignition Signal State | |
|---|---|---|---|---|
Ignition 1 | Ignition 3 | |||
Off | Off-Awake | 0 | 0 | 0 |
Unlock | Off-Awake | 0 | 0 | 0 |
Run | Run | 0 | 1 | 1 |
Crank | Crank | 0 | 1 | 0 |
Accessory | Off-Awake | 0 | 0 | 0 |
Run | Run | 1 | 1 | 1 |
Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the BCM fail to send a power mode message. The fail-safe plan covers modules with discrete ignition signal inputs as well as those modules using exclusively serial data control of power mode.
Serial Data Messages
The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid BCM message until they receive the engine status from the PCM. If the BCM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is true, indicating that the engine is running, the modules fail-safe to "Run". In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is false, indicating that the engine is not running, the modules 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.
Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid BCM 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, B+, the modules will fail-safe to the "RUN" power mode. If the discrete ignition input is not active, open or 0 voltage, 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.
