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CS
BODY CONTROL MODULE (Continued)
Fig. 2 BCM MOUNTING
1 - PARKING BRAKE ASSEMBLY
2 - BCM MOUNTING SCREWS
3 - LOWER STEERING COLUMN
4 - BODY CONTROL MODULE
WARNING: DO NOT CONNECT THE BATTERY NEG-
ATIVE CABLE. (Refer to 8 - ELECTRICAL/RE-
STRAINTS - DIAGNOSIS AND TESTING - AIRBAG
SYSTEM) FIRST.
(7) Verify vehicle and system operation.
COMMUNICATION
DESCRIPTION
The Programmable Communication Interface (PCI)
data bus is a single wire multiplexed network capa-
ble of supporting binary encoded messages shared
between multiple modules. The PCI Bus circuit is
identified as D25 and is white with a violet tracer.
Additional tracer colors may be added to the violet in
order to distinguish between different module con-
nections. The modules are wired in parallel. Connec-
tions are made in the harness using splices.
The modules used include:
• Body Control Module
• Integrated Power Module (IPM)
• Next Generation Controller (NGC)
• Instrument Cluster (IC)
• Electronic Vehicle Information Center (EVIC)
• Occupant Restraint Controller (ORC)
• Compass/Mini-Trip (CMTC)
• Overhead Console
• Controller Antilock Brake (CAB)
• Automatic Temperature Control Module (ATC)
• Power Liftgate Module (PLGM)
ELECTRONIC CONTROL MODULES 8E - 3
• Radio
• CD Changer
• Memory/Heated Seat Adjustable Pedal Module
• Sentry Key RemotE Entry Module (SKREEM)
• Driver Door Module (DDM)
• Passenger Door Module (PDM)
Each module provides its own bias and termination
in order to transmit and receive messages. The bus
voltage is at zero volts when no modules are trans-
mitting and is pulled up to about seven and a half
volts when modules are transmitting.
OPERATION
The PCI bus messages are transmitted at a rate
averaging 10800 bits per second. Since there is only
voltage present when the modules transmit and the
message length is only about 500 milliseconds, it is
ineffective to try and measure the bus activity with a
conventional voltmeter. The preferred method is to
use the DRBIII
scan tool. The 12v square wave
selection on the 20-volt scale provides a good view of
the bus activity. Voltage on the bus should pulse
between zero and about seven and a half volts.
The PCI Bus failure modes are broken down into
two categories. Complete PCI Bus Communication
Failure and individual module no response. Causes of
complete PCI Bus Communication Failure include a
short to ground or battery on the PCI circuit. Indi-
vidual module no response can be caused by an open
circuit at the module, or an open battery or ground
circuit to the affected module.
Symptoms of a complete PCI Bus Communication
Failure would include but are not limited to:
• All gauges on the cluster stay at zero
• All telltales on cluster illuminate
• cluster backlighting at full intensity
• No response received from any module on the
PCI Bus (except the NGC)
• No start (if equipped with Sentry Key Immobi-
lizer)
Symptoms of Individual module failure could
include any one or more of the above. The difference
would be that at least one or more modules would
respond to the DRBIII .
Diagnosis starts with symptom identification. If a
complete PCI Bus Communication Failure is sus-
pected, begin by identifying which modules the vehi-
cle is equipped with and then attempt to get a
response from the modules with the DRBIII . If any
modules are responding, the failure is not related to
the total bus, but can be caused by one or more mod-
ules PCI circuit or power supply and ground circuits.
The DRBIII may display BUS +/- SIGNAL OPEN
or NO RESPONSE to indicate a communication
problem. These same messages will be displayed if
the vehicle is not equipped with that particular mod-
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