Principles of Operation
The vehicle has three module communication networks:
- The standard corporate protocol (SCP) communication 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 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 anti-lock brake system (ABS) module is on the SCP communication network. The module controls brake pressure to the wheels to keep the vehicle under control while braking. See ANTI-LOCK CONTROL - TRACTION CONTROL .
The restraint control module (RCM) control the deployment of the air bags based on sensor input. The RCM is on the ISO 9141 network. See AIR BAG RESTRAINT SYSTEMS .
The overhead console (OHC) is connected to the SCP communication network. The OHC computes and displays in metric or English: average fuel economy, distance to empty, and compass heading. See INFORMATION & MESSAGE CENTER .
The parking aid module is connected to the UBP communication network. The module controls the sensors in the rear bumper that detect close objects when the vehicle is in reverse. See PARKING AID .
The powertrain control module (PCM) is on the SCP communication network. The PCM controls the engine for better fuel economy, emissions control, and failure mode detection and storage. See SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE .
The audio control module (ACM) is on the SCP communication network. See ENTERTAINMENT SYSTEM - GENERAL INFORMATION .
The lighting control module (LCM) is on the SCP communication network. The LCM control both interior and exterior lighting and warning chimes. For interior lighting see INTERIOR LIGHTING . For exterior lighting see EXTERIOR LIGHTING . For warning chimes see WARNING DEVICES .
The hybrid electronic cluster (HEC) is connected to the SCP communication network. The instrument cluster displays driver information, including tachometer reading, fuel level, engine coolant level and speed. See INSTRUMENT CLUSTER .
The telematics control module is connected to the SCP communication network. The telematics control module provides access to a response center that can dispatch emergency and roadside assistance. See VEHICLE EMERGENCY MESSAGE .
The driver seat (DCM) module is connected to the SCP communication network. The DSM controls the driver power seat. In addition, the DSM is programmable to store seat position. See SEATING - TOWN CAR .
The next generation speed control (NGSC) module is on the SCP communication network. The NGSC, when activated, controls and maintains vehicle speed by actuating the throttle linkage. See SPEED CONTROL .
The luggage compartment lid module is on the ISO 9141 network. The module controls the motor that opens and closes the trunk. See BODY CLOSURES .
The driver door module (DDM) is connected to the SCP communication network. The DDM controls the power window, power locks and keyless remote. See HANDLES, LOCKS, LATCHES & ENTRY SYSTEMS .
The rear air suspension module (RASM) is connected to the SCP communication network. The RASM controls the rear ride height. See VEHICLE DYNAMIC SUSPENSION .
The electronic automatic temperature control (EATC) module is connected to the SCP communication network. The EATC module controls automatic climate functions that maintain the vehicle at a constant temperature setting. See CLIMATE CONTROL SYSTEM - GENERAL INFORMATION .