Principles of Operation

PRINCIPLES OF OPERATION

Vehicle communication utilizes a high speed controller area network (HS-CAN), International Standards Organization (ISO) 9141 network and standard corporate protocol (SCP) network. Information is sent to and from individual control modules that each control specific functions. All 4 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 unit.

The 4 module communication networks are:
- ISO 9141
- High speed (HS) CAN
- Standard corporate protocol (SCP)

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.

ISO 9141 Network Communication Fault Chart:

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

Standard Corporate Protocol (SCP) Communication Network

SCP Network Communication Fault Chart:

The SCP network uses an unshielded twisted pair cable of data (+) and data (-) circuits. The data (+) circuit is regulated to approximately 0.5 volts and the data (-) circuits to approximately 4.5 volts during neutral or rested network traffic. Voltage on data circuits increases/decreases as bus messages are sent. Multiple bus messages can be sent over the network SCP circuits allowing network modules to communicate with each other. The SCP network operates at a maximum data transfer speed of 41.6 Kbps and remains operational at a degraded level if one of the bus wires becomes open or shorted to ground or voltage.

HS-CAN
The HS-CAN network 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 network CAN circuits allowing network modules to communicate with each other. The HS-CAN is a high speed communication network used for the instrument cluster, the powertrain control module (PCM), the fire suppression module and anti-lock brake system (ABS) module communication.

The CAN bus (+) and bus (-) circuits must always be terminated. The network termination of the CAN bus takes place inside a "termination module" by termination 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 network 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 when 1 of the 2 termination resistors are not present.

HS-CAN Network Communication Fault Chart:

The fault chart describes the specific HS-CAN network failures and their resulting symptom.

Network Module Communication Message Chart (Part 1):

Network Module Communication Message Chart (Part 2):

Network Module Communication Message Chart (Part 3):

Network Module Communication Message Chart (Part 4):

Network Module Communication Message Chart (Part 5):

The chart describes all network messages broadcast on the SCP and HS-CAN networks and the module(s) that receive the message.