Communications Network

COMMUNICATIONS NETWORK

The module communications network consists of the following items:
- smart junction box (SJB)
- instrument cluster
- powertrain control module (PCM)
- restraints control module (RCM)
- 4-wheel drive (4WD) control module
- anti-lock brake system (ABS) control module

PRINCIPLES OF OPERATION

The vehicle has three module communication networks protocols:
- controller area network (CAN)
- standard corporate protocol (SCP) communication network
- international standards organization (ISO) 9141

The CAN has an unshielded twisted pair cable, data bus plus circuit 1827 (WH/LG) and data bus minus circuit 1828 (PK/LG). The ISO 9141 communications network, which is a single wire network (circuit 70 [LB/WH]), and the standard corporate protocol (SCP), which is an unshielded twisted pair cable, data bus plus, circuit 915 (PK/LB) and data bus minus circuit 914 (TN/OG). 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:
- remote keyless entry (RKE)
- illuminated entry and interior lamps
- power door locks
- windshield wipers
- daytime running lamps
- battery saver
- accessory delay
- power windows

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 915 (PK/LB) and 914 (TN/OG) between the PCM C175 and the DLC C251. 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 C251, damage to the PCM C175, or a problem in the in-line connector.

Passive Anti-Theft System (PATS)
The passive anti-theft system (PATS) is integrated into the PCM. The PCM controls the PATS system functions as well as illumination of the anti-theft indicator. The PCM stores the ignition key codes and controls engine disable.

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.

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.

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.

4-Wheel Drive (4WD) Control Module
The 4-wheel drive (4WD) control module (if equipped) is on the ISO 9141 communication network. The 4WD control module controls the four wheel drive for the vehicle.