Principles and Operation

The vehicle has two module communication networks. The Standard Corporate Protocol (SCP), which is an unshielded twisted pair cable: data bus plus and data bus minus, and the International Standards Organization (ISO) 9141 communications network, which is a single wire network. Both networks can be connected to the diagnostic tool by one connector called the Data Link Connector (DLC). This makes troubleshooting these systems easier by allowing one smart tester to be able to diagnose and control any module on the two networks from one connector. The DLC can be found under the instrument panel, between the steering column and the radio.

The ISO 9141 communication network does not permit inter-module 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 SCP communication 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.

Unlike the SCP communication network, the ISO 9141 communication network will not function if the wire is shorted to ground or voltage. Also, if one of the modules on the ISO 9141 communication network loses power or shorts internally, communications to that module will fail.

The anti-lock brake control module is connected to the SCP communication network. The module comes in three types. The first type is the standard equipped Anti-Lock Brake System (ABS). It controls the brake pressure to the four wheels to keep the vehicle under control while braking. The second type of ABS, if fitted, adds traction control to the anti-lock brake control module. The third type of ABS, if fitted, is called the stability assist module. This module adds yaw rate sensors, lateral accelerometer, and a steering angle rate sensor to the package to help in sensing a loss of vehicle control. All three types use the SCP communication network for diagnosis and communication between other SCP networked modules.

The Audio Control Module (ACM) is connected to the SCP communication network and also to the Audio Control Protocol (ACP) communication network. The ACM communicates with the compact disc player/changer and the cellular phone transceiver.

The Driver Door Module (DDM) is connected to the SCP communication network. The module controls many functions including power windows, power locks, and remote keyless entry. The DDM also communicates with the Driver Seat Module (DSM) to control power seat and mirror memory.

The DSM is connected to the SCP communication network. The DSM controls the driver power seat. The module also communicates with the DDM to control the driver seat memory functions.

The Dual Automatic Temperature Control (DATC) module is connected to the SCP communication network. The DATC module controls automatic climate functions that maintain the vehicle at a constant temperature setting.

The instrument cluster (also known as an Instrument Cluster Module (ICM)) is connected to the SCP communication network. The instrument cluster displays information received on the SCP including speedometer, odometer, fuel, and message center warnings. The instrument cluster also controls the Passive Anti-Theft System (PATS).

The Front Electronic Module (FEM) and Rear Electronic Module (REM) are connected to the SCP communication network. The FEM and REM controls both interior and exterior lighting and active anti-theft functions.

The Powertrain Control Module (PCM) is connected to the SCP communication network. The PCM controls the engine performance, electronic ignition, emission controls, speed control, and on board diagnostics.

The Remote Emergency Satellite Cellular Unit (RESCU) module is connected to the SCP communication network. The module allows a user to request emergency assistance (police, ambulance, fire, wrecker) or directions to a desired location at the touch of a button. Also, if any of the vehicle's airbags are deployed while the RESCU System is powered ON, the system automatically issues a call for emergency assistance.

The Steering Column Lock Module (SCLM) is connected to the SCP communication network. The module controls locking of the steering column and is only equipped on vehicles with manual transmissions.

The Restraint Control Module (RCM) is connected to the ISO 9141 communication network. The RCM controls the deployment of the air bags. and safety belt pretensioners based on sensor input.