Repair and Diagnosis: Testing and Inspection
COMMUNICATIONS NETWORKSmart Junction Box (SJB)
The SJB is on the international standards organization (ISO) 9141 communications network. The SJB is installed on all vehicles. The SJB is a combination of a multifunction control module and a power junction box. The SJB functions control multiple systems which include:
- remote keyless entry (RKE)
- illuminated entry and interior lamps
- power door locks
- windshield wipers
- daytime running lamps
- battery saver
- power windows
Check the ISO 9141 circuit between the SJB J-2280d and the data link connector (DLC) D-01. The 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 ISO 9141 communication network, damage to the DLC D-01, or damage to the SJB J-2280d.
For additional SJB information, see MODULE CONTROLLED FUNCTIONS.
Powertrain Control Module (PCM)
The PCM controls the engine for better fuel economy, emissions control, and failure mode detection and storage.
The PCM is on the standard corporate protocol (SCP) communications network. If one of the bus wires becomes short to ground or voltage, or if some but not all termination resistors are lost, communications can continue. Check circuits (P/LB) and (T/O) between the PCM 0140-175 and the DLC D-01. The 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 communications network, damage to the DLC D-01, damage to the PCM 0140-175, or a problem in the in-line connector.
For additional PCM information, see ELECTRONIC ENGINE CONTROL (EEC) SYSTEM in Troubleshooting.
Restraints Control Module (RCM)
The RCM is on the ISO 9141 communication network. The RCM controls the deployment of the air bags based on sensor input. Check the ISO 9141 network circuit between the RCM 0810-101 and the DLC D-01. The 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 9141 communication network, damage to the DLC D-01, damage to the RCM 0810-101, or a problem in the in-line connector.
For additional RCM information, see AIR BAG AND SAFETY BELT PRETENSIONER SUPPLEMENTAL RESTRAINT SYSTEM (SRS).
Instrument Cluster
The instrument cluster is the only module on the controller area network (CAN). It is an analog face cluster with a digital odometer. The instrument cluster displays a variety of vehicle information. The instrument cluster communicates with the WDS or equivalent tester through the CAN. Check the CAN circuits between the instrument cluster 0922-101 and the DLC D-01. The 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, damage to the DLC D-01, damage to the instrument cluster 0922-101, or a problem in the in-line connector.
For additional instrument cluster information, see INSTRUMENT CLUSTER DIAGNOSTIC TROUBLE CODE (DTC) INDEX. Diagnostic Trouble Code Descriptions
Anti-Lock Brake System (ABS) Module
The ABS module is on the ISO 9141 communications network. The ABS module controls the brake pressure to the 4 wheels to keep the vehicle under control while braking.
For additional ABS module information, see ANTI-LOCK BRAKE SYSTEM (ABS) DIAGNOSIS in Brakes.
Four-Wheel Drive (4WD) Control Module
The 4WD control module (if equipped) is on the ISO 9141 communications network. The 4WD control module controls the vehicle four-wheel drive system.
For additional 4WD control module information, see TRANSFER CASE ELECTRONIC SHIFT ON - BOARD DIAGNOSIS in Driveline System/Axle.
COMMUNICATIONS NETWORK
Principles of Operation
The vehicle has 3 module communications network protocols:
- controller area network (CAN)
- standard corporate protocol (SCP) communications network
- international standards organization (ISO) 9141 communications network
The WDS or equivalent tester connects to the communications networks through the data link connector (DLC). The DLC allows a WDS or equivalent tester access to diagnose and test the vehicle systems of any module on the communications networks.
All 3 communications networks are connected to the DLC. This makes diagnosis and testing of these systems easier by allowing one WDS or equivalent tester to be able to diagnose and control any module on the 3 communications networks from one common connector. The DLC can be found under the instrument panel between the steering column and the driver door.
Controller Area Network (CAN)
The CAN is an unshielded twisted pair cable, data plus circuit (W/LG) and data minus circuit (P/LG). The CAN may be awake when the key is in the OFF position to carry out functions such as accessory delay. In order to do diagnostics, it is necessary to have the key in the ON position.
The CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or the CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If the CAN data minus is shorted to ground or an open exists on either bus line, module-to-module and module-to-tester communication is marginal at best. If there are issues with the CAN, there may be missing functionality and problems connecting with a WDS or equivalent tester.
Standard Corporate Protocol (SCP) Communications Network
The SCP communications network is an unshielded twisted pair cable, data plus circuit (T/O) and data minus circuit (P/LB). The SCP communications network remains operational even with the severing of one of the SCP communications network circuits. If one of the bus wires become shorted to ground or voltage, or if some but not all termination resistors are lost, communications can continue at a degraded level. The SCP communications network allows inter-module communication.
International Standards Organization (ISO) 9141 Communications Network
The ISO 9141 communication network is a single circuit communications network, circuit (LB/W). The ISO 9141 communications network does not permit inter-module communication. When the WDS or equivalent tester communicates to modules on the ISO 9141 communications network, the WDS or equivalent tester must ask for all information; the modules cannot initiate communications.
The ISO 9141 communications network does not function if the circuit is shorted to ground, voltage or a open. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fails.