Jeep Liberty KJ. Manual — part 1483
INSTALLATION
WARNING: To avoid personal injury or death, on vehicles equipped with airbags, disable the supplemental
restraint system before attempting any steering wheel, steering column, airbag, occupant classification sys-
tem, seat belt tensioner, impact sensor, or instrument panel component diagnosis or service. Disconnect
and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge
before performing further diagnosis or service. This is the only sure way to disable the supplemental
restraint system. Failure to take the proper precautions could result in accidental airbag deployment.
NOTE: Before replacing a Body Control Module (BCM), use a diagnostic scan tool to retrieve the current
settings for the many BCM programmable features including electronic pinion factor (tire size), cabin equal-
ization curve (audio system architecture), country code and Remote Keyless Entry (RKE) system prefer-
ences. These settings MUST be programmed into the replacement BCM using the diagnostic scan tool
before returning the vehicle to service. A new BCM is shipped in default mode that may prevent proper
speedometer indications and the availability of numerous electronic features until it has been properly pro-
grammed. Refer to the appropriate diagnostic information.
1. Position the Body Control Module (BCM) (2) to the
Junction Block (JB) (3) and reconnect them at the
JB/BCM interface connector.
2. Install and tighten the four screws (1) that secure
the BCM to the JB. Tighten the screws to 2 N·m
(20 in. lbs.).
3. Reinstall the Junction Block Module (JBM) onto the
instrument panel end bracket. (Refer to 8 - ELEC-
TRICAL/POWER
DISTRIBUTION/JUNCTION
BLOCK - INSTALLATION).
4. Reconnect the battery negative cable.
SPECIFICATIONS
BODY CONTROL MODULE
TORQUE SPECIFICATIONS
DESCRIPTION
N·m
Ft. Lbs.
In. Lbs.
Body Control Module
Mounting Screws
2
-
20
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ELECTRONIC CONTROL MODULES
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COMMUNICATION
DESCRIPTION
The primary on-board communication network between microprocessor-based electronic control modules in this
model is the DaimlerChrysler Programmable Communication Interface (PCI) data bus system. However, some mod-
ules in the vehicle use the Controller Area Network (CAN-C) data bus system in combination with the PCI bus to
form a hybrid bus system. A data bus network minimizes redundant wiring connections; and, at the same time,
reduces wire harness complexity, sensor current loads and controller hardware by allowing each sensing device to
be connected to only one module (also referred to as a node). Each node reads, then broadcasts its sensor data
over the bus for use by all other nodes requiring that data. Each node ignores the messages on the bus that it
cannot use.
The hybrid bus system has a central gateway or hub integral to a Body Control Module/Central GateWay (BCM-
CGW) that is connected to both buses. The gateway physically and electrically isolates the buses from each other
and coordinates the bi-directional transfer of messages between them. The BCM is located on the Junction Block
(JB), which is located on the driver side instrument panel end bracket in the passenger compartment of the vehicle.
The PCI bus is a single-wire multiplex system, while the CAN-C bus is a two-wire multiplex system. Multiplexing is
any system that enables the transmission of multiple messages over a single channel or circuit. Depending upon the
optional equipment in the vehicle, the PCI bus is used for communication between most all body interior nodes,
while the CAN-C bus is used exclusively by certain powertrain and chassis nodes in vehicles equipped with the
hybrid bus.
In addition, certain vehicles may also be equipped with a Serial Controller Interface (SCI) or a K-Line serial link bus
to provide direct diagnostic access between a diagnostic scan tool connected to the industry-standard 16-way Data
Link Connector (DLC) located below the driver side instrument panel and certain powertrain nodes. The Bus Con-
nections table identifies those nodes in this vehicle with more than one possible bus connection configuration.
Those nodes that are not listed in the table are all connected to and accessed through the PCI bus.
BUS CONNECTIONS
NODE
BCM
CAB
ECM
PCM
SAS
TCM
YAW
ALSO KNOWN AS
BCMCGW,
Body
Controller
ABM,
ABS,
ESP
Controller
Diesel
Engine
Controller
NGC,
Gas
Engine
Controller
Steering
Angle
Sensor
EATX,
Transmission
Controller
Yaw,
Lateral G
Sensor
OPTIONS
w/
Central
Gateway
w/ABS
& ESP
Only
w/Diesel
Only
w/Gas
Only
w/ATX
Only
Gas Engine
*COMM
PCI &
CAN
CAN
CAN
CAN
PCI
**CAN
*DIAG
PCI
CAN
CAN
CAN
PCI/SCI
**CAN
*FLASH
PCI
CAN
CAN
CAN
SCI
**CAN
Diesel
Engine
w/MTX
*COMM
PCI &
CAN
CAN
CAN
CAN
**CAN
*DIAG
PCI
CAN
***K-
LINE
CAN
**CAN
*FLASH
PCI
CAN
***K-
LINE
CAN
**CAN
Diesel
Engine
w/ATX
*COMM
PCI &
CAN
CAN
CAN
CAN
**CAN
*DIAG
PCI
CAN
***K-
LINE
CAN
**CAN
*FLASH
PCI
CAN
***K-
LINE
CAN
**CAN
Notes
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ELECTRONIC CONTROL MODULES
8E - 145
BUS CONNECTIONS
NODE
BCM
CAB
ECM
PCM
SAS
TCM
YAW
ALSO KNOWN AS
BCMCGW,
Body
Controller
ABM,
ABS,
ESP
Controller
Diesel
Engine
Controller
NGC,
Gas
Engine
Controller
Steering
Angle
Sensor
EATX,
Transmission
Controller
Yaw,
Lateral G
Sensor
OPTIONS
w/
Central
Gateway
w/ABS
& ESP
Only
w/Diesel
Only
w/Gas
Only
w/ATX
Only
*FUNCTIONS
COMM = Intravehicle Communication
DIAG = Scan Tool Diagnostic Communication
FLASH = Flash Reprogramming Access
**CAN
This is a dedicated CAN-C bus line between the Yaw Sensor and the CAB.
***K-LINE
The K-Line bus may also referred to as the Serial Controller Interface (SCI) bus in some
diagnostic information.
OPERATION
The hybrid bus network allows all electronic modules connected to the bus to share information with each other.
Regardless of whether a message originates from a module on the low speed Programmable Communications Inter-
face (PCI) bus or on the high speed Controller Area Network (CAN-C) bus, the message structure and layout is
similar, which allows the Body Control Module Central GateWay (sometimes referred to as the BCMCGW) to pro-
cess and transfer messages between the buses. The BCMCGW also stores a Diagnostic Trouble Code (DTC) for
certain bus network faults.
All modules (also referred to as nodes) transmit and receive messages over one of these two buses, either the
single-wire PCI bus or the two-wire CAN-C bus. Data exchange between nodes is achieved by serial transmission
of encoded data messages. Each node can both send and receive serial data simultaneously. Bus messages are
carried over the data bus in the form of Variable Pulse Width Modulated (VPWM) signals which, when the high and
low voltage pulses are strung together, form a message. Each node uses arbitration to sort the message priority if
two competing messages are attempting to be broadcast at the same time.
The voltage network used to transmit messages requires biasing and termination. Each module on the bus network
provides its own biasing and termination. Each node terminates the bus through a terminating resistor and a ter-
minating capacitor. There are two types of nodes on the bus. The dominant node terminates the bus through a 1
KW resistor and a 3300 pF capacitor, typically resulting in about a 3300 ohm termination resistance. However, this
resistance value may vary somewhat by application. The BCM (or BCMCGW) is the only dominant node in this
network. A non-dominant (or recessive) node terminates the bus through an 11 KW resistor and a 330 pF capacitor,
typically resulting in about a 10800 ohm termination resistance.
PROGRAMMABLE COMMUNICATIONS INTERFACE DATA BUS
The PCI (or J1850) data bus communication protocol exceeds the Society of Automotive Engineers (SAE) J1850
Standard for Class B Multiplexing. The PCI data bus speed is an average 10.4 Kilobits per second (Kbps).
CONTROLLER AREA NETWORK DATA BUS
The communication protocol being used for the CAN-C data bus is a non-proprietary, open standard adopted from
the Bosch CAN Specification 2.0b. The CAN-C is the faster of the two primary buses in the hybrid bus system
providing near real-time communication (500 Kbps).
The CAN-C bus nodes are connected in parallel to the two-wire bus using a twisted pair, where the wires are
wrapped around each other to provide shielding from unwanted electromagnetic induction, thus preventing interfer-
ence with the relatively low voltage signals being carried through them. The twisted pairs have between 33 and 50
twists per meter. While the CAN bus is operating (active), one of the bus wires will carry a higher voltage and is
referred to as the CAN High or CAN bus (+) wire, while the other bus wire will carry a lower voltage and is referred
to as the CAN Low or CAN bus (–) wire. Refer to the CAN-C bus voltage table.
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ELECTRONIC CONTROL MODULES
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CAN-C Bus Voltages (Normal Operation)
Bus Circuit
Sleep
Recessive
(Bus
Idle)
Dominant
(Bus
Active)
CAN-L
Short to
Ground
CAN-H
Short to
Ground
CAN-L
Short to
Battery
CAN-H
Short to
Battery
CAN-H
Short to
CAN-L
CAN-L (–)
0 V
2.4 - 2.5
V
1.3 - 2.3
V
0 V
0.3 -
0.5V
Battery
Voltage
Battery
Voltage
Less 0.75
V
2.45 V
CAN-H (+)
0 V
2.4 - 2.5
V
2.6 - 3.5
V
0.02 V
0 V
Battery
Voltage
Less 0.75
V
Battery
Voltage
2.45 V
Notes
All measurements taken between node ground and CAN terminal with a standard DVOM.
DVOM will display average network voltage.
Total resistance of CAN-C network can also be measured (60 ohms).
The CAN-C bus network is awake only when the ignition switch is in the On or Start positions. However, an indi-
vidual node on the CAN bus may still be awake with the ignition switch in the Accessory or Unlock positions. This
is because the integrated circuitry of an individual node may be capable of processing certain sensor inputs and
outputs without the need to utilize network resources.
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ELECTRONIC CONTROL MODULES
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