Battery Guard
The battery guard feature provides protection from excessive battery
drain caused by high current loads being accidently left on. Controlling battery
power (Controlled Power Mode) to selected modules up to three days after
each ignition cycle accomplishes this protection.
The Body Control Module (BCM) provides power regulation through the
use of a Low Power Driver and a High Power Control of the battery guard relay
to the following components:
| • | The Radio Interface Module (RIM). |
| • | The Fuel Filler Door Relay coil. |
| • | The Trunk Release Relay coil. |
| • | The Phone (Dealer Installed). |
The battery guard relay supplies the above components with power whenever
the BCM is awake and for 15 minutes after the ignition transitions
to Lock (High Power Mode). The components are supplied a parasitic current
(Low Power Mode) while the BCM is asleep.
The BCM enters the No Controlled Power Mode if the BCM is idle for more
than 3 days. The No Controlled Power Mode turns the Low Power output
Off.
Wake-Up/Asleep States
Wake-Ups are signals that turn the BCM On and cause it to begin active
control and/or monitoring. The High Power Mode activates for a time period
of 15 minutes when the BCM is awakened. The components are restored
with Controlled Power during this time period. After 15 minutes the
BCM transitions to the Low Power and the No Controlled Power Mode.
The following are the wake-up signals:
| • | Any ignition state transition. |
| • | Any of the following with the ignition in the Lock position: |
| - | Any door jamb switch becoming active (i.e. a transition from closed
to open). |
| - | The trunk being opened (i.e. a transition from closed to open). |
| • | A Class 2 RFA-Button report being received. |
The low power current sense feedback is a BCM wake-up. The BCM wakes-up
and enters the High Power Mode when the low power output is active with the
BCM asleep and with the current sense feedback over a threshold of 2.4 amps.
The BCM is asleep when it has stopped monitoring and has become idle.
The BCM deactivates Low Power and transitions to the No Controlled Power Mode
after inactivity of 3 days plus 15 minutes (controlled power
shutdown time). The High and the Low Power are deactivated and remain inactive
until a wake-up is received when the BCM is in the No Controlled Power Mode.
The following occurs before the transition to the No Controlled Power Mode:
| • | The BCM issues a bus wake-up and a Controlled Power Shutdown Report
on the Class 2 bus indicating that the sequence has begun. |
| • | The components powered by the Controlled Power perform necessary
data storage. |
| • | The BCM turns off the Low Power first and then the High Power
Control output a minute after the Class 2 shutdown report. |
Retained Accessory Power (RAP)
The Retained Accessory Power (RAP) feature allows the use of the entertainment/phone
system after the ignition is turned Off. The BCM controls this feature via
the serial data circuit.
The RAP feature disables after the following occurs:
| • | After 10 minutes with the ignition switch in the Lock position. |
| • | With the ignition switch in the Lock position and a door is opened.
The RAP feature will not enable with the door open after the ignition is turned
to the Lock position. |
| • | The ignition switch transistions to the Start position. |
The following are the remaining operations and the features that the
BCM controls:
| • | All door lock/unlock operations including the following features: |
| - | The Remote Keyless Entry. |
| • | The Exterior Lighting Control including the following features: |
| - | The Daytime Running Light. |
| - | The Wiper On Lighting Control. |
| - | The Exterior Lighting Power Control. |
| • | The Delayed Interior Lighting Control. |
| • | The Content Theft Deterrent. |
| • | The various telltale controls in the Instrument Cluster. |
| • | The various telltale controls in the Headlamp Switch. |
| • | The Class 2 diagnostic protocol. |
BCM Replacement
Replace the BCM only if diagnostics in this section directs you specifically
to do so. Most system problems are traceable to faulty wiring, to connectors,
or to components. The BCM itself is very reliable and is not likely the cause
of a fault. Do not replace the BCM before performing a complete diagnosis
or recurrence of the fault will likely occur. Note: Every input to the BCM
is short to ground and short to battery protected. Every output from the
BCM is short to ground and short to battery protected. Therefore, the BCM
does not automatically need to be replaced when there is a short found in
the wiring connected to it. Repair the wiring first, then check the system
for any further problem.
