Communications Network

COMMUNICATIONS NETWORK

Modules monitor and control vehicle subsystems. A module receives input data from various switches, sensors, etc. and then processes the data to control the subsystem functionality. A module contains on-board diagnostics and provides access to the diagnostic information through a communication network.

Module communications network components:
- standard corporate protocol (SCP) communications network
- international standards organization (ISO) communications network
- anti-lock brake system (ABS) module
- four-wheel drive (4WD) control module
- instrument cluster
- powertrain control module (PCM)
- restraint control module (RCM)
- vehicle security module

PRINCIPLES OF OPERATION

The vehicle has two module communication networks:
- international standards organization (ISO) 9141
- standard corporate protocol (SCP)

The diagnostic tool connects to the communication networks through the data link connector (DLC). The DLC allows the diagnostic tool access to diagnose and test the vehicle systems of any module on the networks.

The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates on the ISO 9141 communication network, the diagnostic tool must request all information or initiate module commands. The ISO 9141 communications network will not function if the wire is shorted to ground or voltage.

The SCP communications network uses a twisted wire pair to provide intermodule and diagnostic tool communications. The SCP 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.

The anti-lock brake system (ABS) module communicates on the ISO 9141 network. The ABS module monitors the wheel speed readings from each anti-lock brake sensor and processes this information to determine an impending wheel lock-up. If a wheel lock-up is detected, the ABS module will modulate the brake pressure to the appropriate brake caliper.

The 4-wheel drive (4WD) control module is on the ISO 9141 communication network. The 4WD control module monitors and regulates the four wheel drive operation for the vehicle.

The restraint control module (RCM) communicates on the ISO 9141 network. The RCM monitors and controls the supplemental restraint system (SRS). The SRS is designed to provide increased crash protection for front seat occupants. The RCM will deploy the vehicle air bags based on sensor input during a crash event .

The vehicle security module is on the ISO 9141 communication network. The vehicle security module controls a variety of systems:
- exterior lamps remote keyless entry (RKE) flash and panic
- RKE/keyless entry
- lock/unlock functions

For additional information, refer to Locks for lock/unlock functions or Lighting and Horns for exterior lighting operations.

The powertrain control module (PCM) is hardwired to the SCP network. The PCM receives input from sensors and other electronic components (switches, relays). Based on the information received and programmed into its memory, the PCM generates output signals to control various relays, solenoids and actuators.

The instrument cluster is connected to the SCP communication network. The instrument cluster contains a variety of warning lights and gauges that display vehicle specific information. This allows the driver to continually monitor vehicle conditions.