Communications Network
COMMUNICATIONS NETWORKStandard Corporate Protocol (SCP) Network
The SCP network allows communication between modules through a single vehicle-wide network. A single pair of twisted wires, SCP+ and SCP-, exchange bi-directional data messages between stand-alone modules. Multiple data signals can be transmitted over one circuit. Included in these messages is diagnostic data that is transmitted over the SCP+ and SCP- lines to the data link connector (DLC).
Controller Area Network (CAN)
The CAN network allows communication between the DLC and the diagnostic tool. A single pair of twisted wires, CAN+ and CAN-, exchange bi-directional data messages and allows transmission of multiple diagnostic data signals over one circuit.
International Standards Organization (ISO) Network
The ISO network provides communication between the DLC and the diagnostic tool through a single wire. The ISO network does not permit inter-module communication. The diagnostic tool initiates communication with the module undergoing testing, allowing transmission of diagnostic data to the diagnostic tool through the DLC.
Anti-Lock Brake System (ABS) Module
The ABS module communicates on the SCP 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.
Front Electronic Module (FEM)
The FEM communicates on the SCP network. The FEM is a multi-function module which controls interior and exterior lighting and active anti-theft functions.
Rear Electronic Module (REM)
The REM communicates on the SCP network. The REM is a multi-function module which controls interior and exterior lighting and active anti-theft functions.
Restraint Control Module (RCM)
The 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.
Instrument Cluster
The instrument cluster communicates on the SCP 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.
Remote Keyless Entry (RKE) Module
The RKE module communicates on the SCP network. The remote door locks and luggage compartment lid are controlled by the RKE module.
Powertrain Control Module (PCM)
The PCM is hardwired to two communication networks. Diagnostic data is provided through the CAN network to the diagnostic tool. Stand-alone modules exchange information with the PCM through 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.
Dual Automatic Temperature Control (DATC) Module
The DATC module communicates on the SCP network. The DATC system automatically maintains a selected temperature for vehicle interior comfort and regulates the volume of airflow between the instrument panel registers, floor ducts, windshield defroster nozzle, and side window demisters.
Audio Control Module (ACM)
The ACM communicates on the SCP network. The ACM monitors the audio unit inputs. Based on these inputs, the ACM generates output signals to control the various audio system components which are designed to provided maximum listening pleasure.
PRINCIPLES OF OPERATION
Multi Function Modules
The vehicle's electronic functions are divided into zones. The FEM controls the front portion of the vehicle and the REM controls the rear portion of the vehicle. These systems rely heavily on the SCP communication network in order to transmit and receive signals. As a technician, it is very important to understand:
- where the input (command) originates from.
- all information (messages) necessary in order for a feature to operate.
- which module(s) receive(s) the input or command message.
- whether the module which received the input (message) controls the output of the feature, or whether it outputs a message over the SCP communication network to another module.
- which module controls the output of the feature.
Communications Network
The CAN communications network is a high speed communication network used for powertrain communication. The CAN 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.
The SCP communications network will remain operational even with the severing of one of the bus wires. Communication will 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 will not function if the single bus wire is shorted to ground or voltage.