Principles of Operation

PRINCIPLES OF OPERATION

Vehicle communication utilizes a high speed controller area network (HS-CAN), International Standards Organization (ISO) 9141 network and universal asynchronous receiver/transmitter (UART) based protocol (UBP) network. Information is sent to and from individual control modules that each control specific functions. All 3 networks are connected to the data link connector (DLC). The DLC can be found under the instrument panel between the steering column and the audio control module (ACM).

The 3 module communication networks are:
- High speed (HS) CAN
- ISO 9141
- UBP

ISO 9141 Communications Network
The ISO 9141 communications network is a single wire network. The ISO 9141 communications network does not permit intermodule communication. When the scan tool communicates to modules on the ISO 9141 communication network, the scan tool must request all information; the modules cannot initiate communications. The ISO 9141 network operates at a maximum data transfer speed of 10.4 Kbps.

The following modules are on the ISO 9141 network:
- Parking aid module (PAM) (if equipped)
- Restraints control module (RCM)

The following fault chart describes the specific ISO 9141 network failures and their resulting symptom:

ISO 9141 Network Communication Fault Chart:

HS-CAN
The HS-CAN uses an unshielded twisted pair cable of data (+) and data (-) circuits. The data (+) and the data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As bus messages are sent on the data (+) circuit, voltage is increased by approximately 1.0 volt. Inversely, the data (-) circuit is reduced by approximately 1.0 volt when a bus message is sent. Multiple bus messages can be sent over the CAN circuits allowing network modules to communicate with each other.

The CAN bus (+) and bus (-) circuits must always be terminated. The network termination of the CAN bus takes place inside the 2 termination modules, the PCM and the instrument cluster (IC), by resistors rated at 120 ohms, located across the (+) and (-) circuits. The resistors are wired in parallel to the network bus circuits for a total operating resistance of 60 ohms on a good network.

The HS-CAN operates at a maximum data transfer speed of 500 Kbps and remains operational at a degraded level when certain circuit faults are present. The HS-CAN bus may remain operational with only one termination resistor present.

The following modules are on the HS-CAN:
- ABS module
- IC
- PCM with integrated 4X4 control module

The following fault chart describes the specific HS-CAN failures and their resulting symptom:

HS-CAN Communication Fault Chart:

Universal Asynchronous Receiver-Transmitter (UART)-Based Protocol (UBP) Communications Network
The UBP communications network is a single circuit communications network, circuit 1906 (VT). The UBP communications network does not function if the wire is shorted to ground or voltage. The UBP communications network allows intermodule communication. The UBP network operates at a maximum data transfer speed of 9.6 Kbps. The UBP network circuit is regulated to approximately 12.0 volts during neutral or rested network traffic. This voltage is reduced proportional to the volume of bus messages sent.

The following modules are on the UBP network:
- Heating ventilation air conditioning (HVAC) module (if equipped)
- Driver seat module (DSM) (if equipped)
- Instrument cluster (IC)
- Vehicle security module (VSM)

The following fault chart describes the specific UBP network failures and their resulting symptom:

UBP Network Communication Fault Chart:

The following chart describes all network messages broadcast on HS-CAN, SCP and UBP by each module, and the module(s) that receive the message:

Network Module Communication Message Chart (Part 1):

Network Module Communication Message Chart (Part 2):