Communications Network

COMMUNICATIONS NETWORK

The module communications network consists of the following items:
- powertrain control module (PCM)
- natural gas alternative fuel control module (AFCM)
- instrument cluster
- restraint control module (RCM)
- anti-lock brake system (ABS) module
- vehicle security module

PRINCIPLES OF OPERATION

The vehicle has 3 module communication network protocols:
- standard corporate protocol (SCP) communication network
- international standards organization (ISO) 9141
- controller area network (CAN) (diesel only)

The SCP is an unshielded twisted pair cable, data bus plus, circuit 915 (PK/LB) and data bus minus circuit 914 (TN/OG). The ISO 9141 communications network is a single wire network circuit 70 (LB/WH). The CAN is an unshielded twisted pair cable, data bus, circuit 3022 (PK/YE) and circuit 3073 (RD/WH). All networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one diagnostic tool to be able to diagnose and control any module on the networks from one connector. The DLC can be found under the instrument panel and the steering column.

The SCP and CAN 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 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 ask for all information; the modules cannot initiate communications. 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.

Powertrain Control Module (PCM) (Gasoline)
The PCM is on the SCP communication network. The PCM controls the engine for better fuel economy, emissions control, failure mode detection and storage. If one of the bus wires becomes shorted to ground or voltage, or if some but not all termination resistors are lost, communications can continue. Check circuits 915 (PK/LB) and 914 (TN/OG) between the PCM C175 and the DLC C251. Total resistance values must not be more than 5 ohms. If the resistance is more than 5 ohms there is an open circuit in the SCP network, damage to the DLC C251, damage to the PCM C175, or a problem in the in-line connector.

Powertrain Control Module (PCM) (Diesel)
The PCM is on the CAN communication network. The PCM controls the engine for better fuel economy, emissions control, failure mode detection and storage. If one of the bus wires becomes shorted to ground or voltage, or if some but not all termination resistors are lost, communications can continue. Check circuits 3072 (PK/YE) and 3073 (RD/WH) between the PCM C176a and the DLC C251. Total resistance values must not be more than 5 ohms. If the resistance is more than 5 ohms there is an open circuit in the CAN network, damage to the DLC C251, damage to the PCM C176a, or a problem in the in-line connector.

Natural Gas Alternative Fuel Control Module (AFCM)
The AFCM is on the SCP communication network. The AFCM controls the fuel and ignition systems for better fuel economy, emissions control, failure mode detection and storage. If one of the bus wires becomes shorted to ground or voltage, or if some but not all termination resistors are lost, communications can continue. Check circuits 915 (PK/LB) and 914 (TN/OG) between the AFCM C1009 and the DLC C251. Total resistance values must not be more than 5 ohms. If the resistance is more than 5 ohms there is an open circuit in the SCP network, damage to the DLC C251, damage to the AFCM C1009, or a problem in the in-line connector.

Instrument Cluster
The instrument cluster is on the SCP communications network. It is an analog face cluster with a digital odometer. The instrument cluster displays a variety of information. Check circuits 915 (PK/LB) and 914 (TN/OG) between the instrument cluster C220a and the DLC C251. Total resistance values must not be more than 5 ohms. If the resistance is more than 5 ohms there is an open circuit in the SCP network, damage to the DLC C251, damage to the instrument cluster C220a, or a problem in the in-line connector.

Restraint Control Module (RCM)
The RCM is on the ISO 9141 network. The RCM controls the deployment of the air bags based on sensor input. The ISO communication network will not function if the wire is shorted to ground or battery voltage. Check the network circuit between the RCM C310a and the DLC C251. Total resistance value must not be more than 5 ohms. If the resistance is more than 5 ohms, there is an open circuit in the ISO network, damage to the DLC C251, damage to the RCM C310a, or a problem in the in-line connector.

Anti-Lock Brake System (ABS) Module
The ABS module is on the ISO 9141 communication network. The ABS module controls the brake pressure to the four wheels to keep the vehicle under control while braking. The ISO communication network will not function if the wire is shorted to ground or battery voltage. Check the network circuit between the ABS module C135 and the DLC C251. Total resistance value must not be more than 5 ohms. If the resistance is more than 5 ohms, there is an open circuit in the ISO network, damage to the DLC C251, damage to the ABS C135, or a problem in the in-line connector.

Vehicle Security Module
The vehicle security module is on the ISO 9141 network. The vehicle security module controls the remote keyless entry (RKE) function as well as the power door locks. The ISO communication network will not function if the wire is shorted to ground or battery voltage. Check the network circuit between the vehicle security module C203b and the DLC C251. Total resistance value must not be more than 5 ohms. If the resistance is more than 5 ohms, there is an open circuit in the ISO network, damage to the DLC C251, damage to the vehicle security module C203b, or a problem in the in-line connector.