Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 3 module communications networks:
- controller area network (CAN)
- international standards organization (ISO) 9141 communications network
- universal asynchronous receiver-transmitter (UART) based protocol (UBP) communications network

The diagnostic tool connects to the communications networks through the data link connector (DLC). The DLC allows a diagnostic tool access to diagnose and test the vehicle systems of any module on the communications networks.

The CAN has an unshielded twisted pair cable, data plus circuit 1908 (WH) and data minus circuit 1909 (BK). The CAN is a communications network used for the anti-lock brake system (ABS) module, the instrument cluster, powertrain control module (PCM) and the trailer brake controller communications. The CAN remains operational even with the severing of one of the CAN circuits but operates at a degraded level. Communications also continue at a degraded level if one of the CAN circuits are shorted to ground or voltage, or if some but not all termination resistors are lost.

The ISO 9141 communications network is a single circuit communications network, circuit 70 (LB/WH). The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communications network, the diagnostic tool must request all information or initiate module commands. The ISO 9141 communications network is a communications network used for the 4-wheel drive (4WD) control module, the parking aid module and the restraint control module (RCM) communications. The ISO 9141 communications network does not function if the circuit is shorted to ground or voltage. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fail.

The UBP communications network is a single circuit communications network, circuit 693 (OG). The UBP communications network is a communications network used for the electronic automatic temperature control (EATC) module, the instrument cluster and the vehicle security module communications. The UBP communications network does not function if the circuit is shorted to ground or voltage. The UBP communications network is different from the ISO 9141 communications network in that it allows intermodule communication.

4WD Control Module
The 4WD control module (if equipped) uses the ISO 9141 communications network. The 4WD control module monitors and regulates the 4-wheel drive operation for the vehicle.

ABS Module
The ABS module uses the CAN. 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 modulates the brake pressure to the appropriate brake caliper.

EATC Module
The EATC module (if equipped) uses the UBP communications network. The EATC module controls the automatic climate functions to maintain the vehicle at a constant temperature setting.

Instrument Cluster
The instrument cluster uses the UBP communications network and the CAN. Diagnostic data is supplied through the CAN to the diagnostic tool. The instrument cluster serves as a communications network gateway between the CAN and the UBP communications network for internetwork module communication. 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.

Parking Aid Module
The parking aid module (if equipped) uses the ISO 9141 communications network. The module monitors sensors mounted in the rear bumper that detect the proximity of objects to the vehicle when the vehicle is in reverse.

PCM
The PCM uses the CAN. 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.

RCM
The RCM uses the ISO 9141 communications 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 deploys the vehicle air bags based on sensor input during a crash event.

Trailer Brake Controller
The trailer brake controller (if equipped) uses the CAN. The trailer brake controller operates the trailer brakes.

Vehicle Security Module
The vehicle security module uses the UBP communications network. The vehicle security module controls:
- remote keyless entry (RKE)
- exterior lamps (RKE flash and panic)
- lock/unlock functions