Body Control Module General Description
Familiarize yourself with the information and proper diagnosing procedures
before using this section of the manual. This section contains a body control
module (BCM) diagnostic system check. The BCM diagnostic system check is
an organized approach in order to identify the cause of a condition that
is reported by a BCM system malfunction code.
The BCM diagnostic system check is the starting point for diagnosis
of any BCM system complaint. The BCM diagnostic system check will direct you
to the next logical step in diagnosing the complaint. Correct use of the
table reduces diagnostic time and prevents unnecessary replacement of good
parts.
Body Control Module System Description
The BCM is designed in order to perform the following functions:
| • | Process various input information |
| • | Send the needed electrical responses to the other control modules |
The input information is related to more than one output. If one input
fails, the failure may affect the operation of more than one system.
The BCM controls the operation of the following components:
The BCM has features that permit the following functions:
| • | Timing out and turning OFF inadvertent loads |
| • | Providing retained accessory power |
The BCM is designed in order to interface with a remote function actuator
(RFA) subsystem. The interface provides remote operation of certain features
of the vehicle. The BCM also provides vehicle security with an integrated
Passlock system.
The BCM communicates via a Class 2 serial data bus. The communication
enables diagnosis and programming at the assembly plant or an approved service
center.
The BCM supplies a buffered voltage to various sensors and switches
through an internal resistance in the BCM. The resistance is so high in value
that an ordinary test lamp may not light when the lamp is connected to the
circuit. An ordinary shop voltmeter may give an inaccurate reading because
the voltmeter input impedance is too low. Use a J 39200
Digital Multimeter (DMM) in order to ensure accurate voltage
readings. Refer to
Special Tools
.
Body Control Module Service Precautions
Do not use a test lamp in order to diagnose the BCM electrical system
unless you are specifically instructed by diagnostic procedures. Use the J 35616-A
when diagnostic procedures
require probing of connectors. Refer to
Special Tools
.
The BCM will withstand normal current draws associated with vehicle
operations. Avoid overloading any circuit. When testing for opens or shorts,
do not ground or apply voltage to the BCM circuits unless you are instructed
to do so. These circuits may only be tested using a J 39200
Digital Multimeter (DMM) or equivalent. Test electrical circuits
using a J 39200
DMM, while
the BCM connectors remain connected to the BCM or the recommended breakout
box. Do not remove or apply voltage to the BCM when the ignition switch is
in the RUN position. Turn the ignition switch to the LOCK position before
removing or connecting any of the following electrical components:
Follow the instructions in this section whenever a BCM removal or replacement
procedure is performed.
When servicing the BCM system, use the following guidelines:
| • | Always DISCONNECT the brown (BRN) BCM connector FIRST. |
| • | Always CONNECT the brown (BRN) BCM connector LAST. |
The BCM may set codes when the ignition switch is in the OFF position.
Disconnecting the electrical connectors from the BCM will set DTC(s).
The BCM may require a 20 minute (1216 second) time period
in order to power down when all of the following conditions exist:
| • | The ignition switch is turned to the OFF position. |
| • | The BCM is not receiving any active inputs. |
| • | The BCM does not receive any active inputs for 20 minutes. |
