Circuit Operation
This section is intended to provide the technician with an understanding
of the body control module (BCM) operation. The BCM systems listed
below are not described in detail in this section. For a detailed circuit
description, refer to the following proceduresRefer to the following circuit
descriptions for more detail:
Wake-up and Sleep Modes
Wake-up signals are signals which turn on the BCM. Once active, the
BCM begins monitoring and controlling the system functions listed above. With
the ignition switch in the OFF position, the BCM ceases control of the system
functions after a 10 minute period. This is the sleep mode. During
the sleep mode the BCM monitors several circuits for changes in status. The
BCM wakes up when a change is detected in any of the following inputs:
• | The remote keyless entry system |
• | The rear compartment lid ajar indication switch |
• | The ignition key lock cylinder |
• | The theft deterrent shock sensor |
Power Requirements
The BCM will operate properly with a system voltage of 9-16 volts.
Operating current measured at the BCM battery terminals in the awake
mode should not exceed the following values:
• | 75 milliamps with the ignition switch in the OFF position |
• | 250 milliamps with the ignition switch in the RUN position |
Operating current measured at the BCM battery terminals in the sleep
mode should not exceed the following values:
• | Two milliamps on vehicles without theft deterrent (UA6) |
• | Three milliamps on vehicles with theft deterrent (UA6) |
Operating current measured at the BCM IGN1 and IGN3 terminals should
not exceed 15 milliamps.
Abbreviations
The following abbreviations are used throughout this section:
• | Body control module (BCM) |
• | Data link connector (DLC) |
• | Diagnostic trouble code (DTC) |
• | Digital multimeter (DMM) |
• | Powertrain control module (PCM) |
• | Personal automotive security system (PASS-Key® II) |
• | Retained accessory power (RAP) |
• | Universal theft deterrent (UTD) |
BCM Replacement
Technicians should not replace the BCM unless directed to do so by the
diagnostic procedures in this section. Most system faults are traceable to
faulty wiring, connectors or components. The BCM is very reliable and is
not likely the cause of the fault. Do not replace the BCM before performing
a complete diagnosis. This may result in the replacement of a good BCM and
a recurrence of the fault.
Important:
• | A new BCM is shipped from the supplier in the factory test mode.
This mode allows only limited functionality of the BCM controlled systems.
When a new BCM is installed it is necessary to exit the factory test mode
prior to returning the vehicle to the customer. To restore the BCM to normal
operation, turn the ignition switch from the RUN position to the OFF position
10 times or enter the program mode as described in the theft deterrent system. |