Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has three module communication networks:
- medium speed controller area network (CAN)
- high speed controller area network (CAN)
- international standards organization (ISO) 9141

The medium speed CAN has an unshielded twisted pair cable, data bus plus circuit 1827 (WH/LG) and data bus minus, circuit 1828 (PK/LG). The high speed CAN also has an unshielded twisted pair cable, data bus plus circuit 1847 (WH/OG) and data bus minus, circuit 1848 (PK/OG). The ISO 9141 communications network, which is a single wire network, circuit 70 (LB/WH). 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 audio unit.

The high speed CAN is a high speed communication network used for instrument cluster, powertrain control module (PCM) and anti-lock brake system (ABS) module communication. The medium speed CAN is used for smart junction box (SJB) and electronic automatic temperature control (EATC) module communications. The CAN 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.

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 ISO communication network is used to communicate with the restraints control module (RCM).

Anti-Lock Brake System (ABS) Module
The ABS module (if equipped) is on the high speed CAN.The high speed CAN is utilized by the ABS control module for communicating with the diagnostic tool. The ABS module controls the brake pressure to the four wheels to keep the vehicle under control while braking.

Electronic Automatic Temperature Control (EATC) Module
The EATC module is located in the instrument panel below the audio unit. The EATC module is on the medium speed CAN. The EATC module controls automatic climate functions that maintain the vehicle interior temperature at a constant setting.

Smart Junction Box (SJB)
The SJB is on the medium speed CAN. The SJB is equipped on all vehicles. The SJB is a combination of a multifunction control module and an interior power junction box. SJB functions control multiple systems which include:
- speed dependent interval windshield wipers
- illuminated entry and interior lamps
- power door locks
- windshield wipers
- warning chimes
- battery saver
- accessory delay
- power window

Restraints Control Module (RCM)
The RCM is the only module on the ISO 9141 network. The RCM controls the deployment of the air bags based on sensor input.

Powertrain Control Module (PCM)
The PCM is on the high speed CAN. The PCM controls the engine for better fuel economy, emissions control, failure mode detection and storage. Refer to Computers and Control systems for diagnosis and testing of the PCM.

Passive Anti-Theft System (PATS)
The 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.

Instrument Cluster
The instrument cluster is on the high speed CAN. It is an analog face cluster with a digital odometer. The instrument cluster displays a variety of information.