Information Bus: Description and Operation

NETWORKING: CAN COMMUNICATION SYSTEM

SYSTEM DIAGRAM









SYSTEM DESCRIPTION

1. BRIEF DESCRIPTION
(a) The CAN (Controller Area Network) is a serial data communication system for real time application. It is a vehicle multiplex communication system which has a high communication speed and the ability to detect malfunctions.
(b) By pairing the CANH and CANL bus wires, the CAN performs communication based on differential voltage.
(c) Many ECUs (sensors) installed on the vehicle operate by sharing information and communicating with each other.
(d) The CAN has two resistors of 120 Ohms which are necessary to communicate with the main bus wire.
2. DEFINITION OF TERMS
(a) Main bus wire
(1) The main bus wire is a wire harness between the two terminating resistors on the bus (communication wire). This is the main bus in the CAN communication system.
(b) Branch wire
(1) The branch wire is a wire harness which diverges from the main bus wire to an ECU or sensor.
(c) Terminating resistors
(1) Two resistors of 120 Ohms are installed in parallel across the ends of the CAN main bus wire. They are called terminating resistors. These resistors allow the changes of the voltage differential between the CAN bus wires to be accurately judged. To allow proper function of CAN communication, it is necessary to have both terminating resistors installed. Since the two resistors are installed in parallel, a measurement of resistance between the two CAN bus wires should produce a reading of approximately 60 Ohms.
3. CIRCUIT DESCRIPTION
(a) The CAN No. 1 bus and CAN No. 2 bus bus each has terminus circuits with 120 Ohms x 2 of resistance. High speed communication at 500 kbps is possible.
4. ECUS OR SENSORS WHICH COMMUNICATE THROUGH CAN COMMUNICATION SYSTEM
(a) Skid control ECU
(b) Yaw rate sensor
(c) Steering angle sensor
(d) Main body ECU
(e) Center airbag sensor assembly
(f) ECM
(g) Air conditioning amplifier (w/ air conditioning system)
(h) Combination meter
(i) Power steering ECU
(j) Network gateway ECU (for 4WD)
(k) 4WD control ECU (for 4WD)
(l) Accessory gateway
5. DIAGNOSTIC CODE FOR CAN COMMUNICATION SYSTEM
(a) DTCs for the CAN communication system are as follows: U0073, U0100, U0123, U0124, U0126, U0129*1, U0114*1, U1002*2 and B1499*2.
*1: for 4WD
*2: w/ Air conditioning system
6. TROUBLESHOOTING REMARKS
(a) DTCs for the CAN communication system can be checked using the Techstream. The DLC3 is connected to the CAN communication system, but no DTCs exist regarding problems in the DLC3 or the DLC3 branch wires. If there is trouble in the DLC3 or the DLC3 branch wires, ECUs on the CAN network cannot output codes to the Techstream.
(b) Trouble in the CAN buses (communication wires) can be checked by measuring the resistance between terminals of the DLC3. However, an open circuit in a branch wire other than the DLC3 branch wires cannot be checked from the DLC3.
NOTE: Do not insert the Techstream probes directly into the DLC3. Be sure to use service wires.