Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has three module communication networks:
- the standard corporate protocol (SCP) communications network
- the international standards organization (ISO) 9141 communications network
- the UART based protocol (UBP) communications network

The diagnostic tool connects to all three networks through the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one smart tester 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 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 request all information; or initiate module commands.

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. The SCP communications network allows inter-module communication.

The UBP communications network will not function if the wire is shorted to ground or voltage. The UBP is different from the ISO communication network in that it allows intermodule communication.

The powertrain control module (PCM) is connected on the SCP communication network. The PCM controls the engine performance, electronic ignition, emission controls and on-board diagnostics. Refer to Computers and Control Systems. The passive anti-theft system (PATS) is integrated into the PCM. The PCM controls the PATS functions as well as illumination of the anti-theft indicator. The illumination command is sent from the PCM through the SCP communications network to the instrument cluster, which in turn sends power to the antitheft indicator. The PCM stores the ignition key codes and controls engine disable.The vehicle speed control is integrated into the PCM. The PCM controls the system functions as well as illumination of the speed control indicator located in the instrument cluster. The illumination command is sent from the PCM through the SCP communications network to the instrument cluster, which in turn sends power to the speed control indicator.

The dual electronic automatic temperature control (DEATC) module (if equipped) is connected to the SCP communication network. The DEATC module controls automatic climate functions that maintain the vehicle at a constant temperature setting. Refer to Heating and Air Conditioning.

The instrument cluster is connected to the SCP and UBP communication networks. The instrument cluster displays driver information, including tachometer reading, fuel level, engine coolant level and speed. The message center is included in the high option level cluster and displays door/hatch ajar information, lamp outage and low washer fluid level. Refer to Instrument Panel, Gauges and Warning Indicators.

The 4-wheel anti-lock brake (4WABS) control module is connected to the ISO 9141 and the SCP communication networks. The module controls the brake pressure to the four wheels to keep the vehicle under control while braking. The module also controls the traction control system. The module controls wheel spin by modulating the engine torque and by applying, then releasing, the appropriate front brake to restore traction when driving on slippery or loose surfaces. Refer to Antilock Brakes/Traction Control Systems.

The driver seat module (DSM) (if equipped) is connected to the UBP communication network on late build vehicles, and the ISO 9141 communication network on early build vehicles. The DSM controls the driver power seat. In addition, the DSM is programmable to store seat position and pedal position. Refer to Seats.

The parking aid module (if equipped) is connected to the ISO 9141 communication network. The module controls sensors in the rear bumper that detect close objects when the vehicle is in reverse. Refer to Collision Avoidance and Parking Assist Systems.

The restraint control module (RCM) is connected to the ISO 9141 communication network. The RCM controls the deployment of the air bags based on sensor input. Refer to Air Bag Systems.

The 4-wheel drive (4WD) control module (if equipped) is on the UBP communication network on late build vehicles, and on the ISO 9141 communication network on early build vehicles. The 4WD control module controls the four wheel drive functions for the vehicle. Refer to Transfer Case.

The vehicle security module (late build) is on the UBP communication network. The vehicle security module controls a variety of systems:
- autolamps
- perimeter security
- RKE/keyless entry
- lock functions
- monitors the entry doors

Disconnect the battery before removal of any vehicle security module connectors.

The tire pressure monitoring system module (if equipped) is connected to the SCP communication network. The module uses four sensors to monitor air pressure in the tires. If the tire pressure is low, the sensors transmit a signal using radio waves to the module. The module will then send the information to the message center to notify the driver. Refer to Wheels, Tires, and Alignment.

The generic electronic module (GEM) (early build) is on the UBP communication network. The GEM controls a variety of systems:
- windshield wipers
- courtesy lamps
- warning chimes
- interior lamps
- exterior lamps
- power windows

The central security module (early build) is on the UBP communication network. The central security module controls perimeter security, RKE/keyless entry, and lock functions for the vehicle. The central security module monitors the entry doors. In addition the central security module controls the keyless entry functions. Refer to Body Control Systems (Multifunction Electronic Control Module).

Disconnect the battery before removal of any central security module connectors.