Information Bus: Description and Operation
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 C2280d and the data link connector (DLC) C251. 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 C251, or damage to the SJB C2280d.
For additional SJB information, refer to Body Control Systems (Multifunction Electronic Control Module).
Powertrain Control Module (PCM)
The PCM controls the engine for better fuel economy, emissions control, failure mode detection and storage, and all passive anti-theft system (PATS) functions.
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 915 (PK/LB) and 914 (TN/OG) between the PCM C175 and the DLC C251. 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 C251, damage to the PCM C175, or a problem in the in-line connector.
For additional PATS information, refer to Antitheft and Alarm Systems.
For additional PCM information, refer to Computers and Control Systems.
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 C2041 and the DLC C251. 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 C251, damage to the RCM C2041, or a problem in the in-line connector.
For additional RCM information, refer to Air Bag Systems.
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 diagnostic tool through the CAN. Check the CAN circuits between the instrument cluster C220b and the DLC C251. 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 C251, damage to the instrument cluster C220b, or a problem in the in-line connector.
For additional instrument cluster information, refer to Instrument Panel, Gauges and Warning Indicators.
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, refer to Antilock Brakes/Traction Control Systems.
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 4-wheel drive system.
For additional 4WD control module information, refer to Transfer Case.