B4000 V6-4.0L SOHC (2005)
Body Control Systems: Description and Operation
Communications Network
COMMUNICATIONS NETWORK DIAGNOSIS
Principles of Operation
The vehicle has three module communication networks protocols:
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controller area network (CAN)
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standard corporate protocol (SCP) communication network
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international standards organization (ISO) 9141
The CAN has an unshielded twisted pair cable, data bus plus circuit W/LG and data bus minus circuit P/LG. The ISO 9141 communications network,
which is a single wire network (circuit LB/W), and the standard corporate protocol (SCP), which is an unshielded twisted pair cable, data bus plus,
circuit P/LB and data bus minus circuit T/O. All three networks are connected to the data link connector (DLC). This makes diagnosis and testing of
these systems easier by allowing one diagnostic tool to be able to diagnose and control any module on the three networks from one connector. The DLC
can be found under the instrument panel between the steering column and the radio.
The CAN communications network is a high speed communication network used for diagnostic communication.
The CAN communication network will operate in a degraded mode with the severing of one of the bus wires. Communications will also operate in a
degraded mode if one of the bus wires is shorted to ground or voltage, or if some but not all termination resistors are lost.
The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO
9141 communication network, the diagnostic tool must ask for all information; the modules cannot initiate communications. The ISO 9141
communications network will not function if the wire is shorted to ground or battery voltage. Also, if one of the modules on the ISO 9141
communications network loses power or shorts internally, communications to that module will fail.
The SCP communications network will remain operational even with the severing of one of the bus wires. Communications will also continue if one of
the bus wires is shorted to ground or voltage, or if some but not all termination resistors are lost.
Smart Junction Box (SJB)
The smart junction box (SJB) is on the ISO 9141 network. The SJB is equipped on all vehicles. The SJB is a combination of a multifunction control
module and a power junction box. SJB functions control multiple systems which include:
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remote keyless entry (RKE)
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illuminated entry and interior lamps
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power door locks
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windshield wipers
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daytime running lamps
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battery saver
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accessory delay
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power windows
SMART JUNCTION BOX (SJB) DIAGNOSIS.
Powertrain Control Module (PCM)
The PCM is the only module on the SCP communication network. If one of the bus wires becomes shorted to ground or voltage, or if some but not all
termination resistors are lost, communications can continue. Check circuits P/LB and T/0 between the PCM 0140-175 and the DLC 0-01. Total
resistance values must not be more than 5 Ohms. If the resistance is more than 5 Ohms there is an open circuit in the SCP network, damage to the DLC
0-01, damage to the PCM 0140-175, or a problem in the in-line connector.
Restraints Control Module (RCM)
The restraints control module (RCM) is on the ISO 9141 network. The RCM controls the deployment of the air bags based on sensor input. See AIR
BAG SYSTEM ON - BOARD DIAGNOSIS, for additional information.
Instrument Cluster
The instrument cluster is the only module on the CAN communications network. It is an analog face cluster with a digital odometer. The instrument
cluster displays a variety of information. See INSTRUMENT CLUSTER DIAGNOSIS,for additional information.
Anti-Lock Brake System (ABS) Control Module
The anti-lock brake system (ABS) control module is on the ISO 9141 communication network. The ABS control module controls the brake pressure to
the four wheels to keep the vehicle under control while braking. See ANTI-LOCK BRAKE SYSTEM (ABS) DIAGNOSIS, for additional information.
