System Description
NETWORKING: CAN COMMUNICATION SYSTEM: SYSTEM DESCRIPTION
1. BRIEF DESCRIPTION
(a) The Controller Area Network (CAN) 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) Using the CANH and CANL bus lines as a pair, CAN communication is performed using a voltage differential. (A base voltage is applied to the pair of lines and a voltage differential is created when communicating.)
(c) Many ECUs or 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 enable communication.
(e) Control system CAN is composed of 3 buses.
2. DEFINITION OF TERMS
(a) Main bus
(1) The main bus is a wire harness between the two terminating resistors on the bus. This is the main bus in the CAN communication system.
(b) Branch
(1) The branch is a wire harness which diverges from the main bus 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 lines. They are called terminating resistors. These resistors allow the changes of the voltage differential between the CAN bus lines 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, this results in a measurement of approximately 60 Ohms.
3. ECUS OR SENSORS WHICH COMMUNICATE THROUGH CAN COMMUNICATION SYSTEM
(a) V Bus
(1) ECM
(2) Brake booster with master cylinder assembly (Skid control ECU)
(3) Main body ECU (Multiplex network body ECU)
(4) Yaw rate sensor
(5) Power steering ECU assembly
(6) Smart key ECU assembly (Certification ECU)
(7) Airbag ECU assembly
(8) Spiral cable with sensor sub-assembly (Steering angle sensor)
(9) Power management control ECU
(10) Transmission control ECU assembly
(11) Meter circuit plate
(12) Navigation computer sub-assembly*1
(13) Radio and display receiver assembly*2
(b) Sub bus 11
(1) Power management control ECU
(2) Driving support ECU assembly*3
(3) Seat belt control ECU*4
(4) Parking assist ECU*5
(c) Sub bus 12
(1) Power management control ECU
(2) ECM
(3) Brake booster with master cylinder assembly (Skid control ECU)
(4) Air conditioning amplifier assembly
HINT
*1: for Navigation receiver type
*2: for Radio and display type
*3: w/ Dynamic radar cruise control system
*4: w/ Pre-collision system
*5: w/ Advanced parking guidance system
4. CIRCUIT DESCRIPTION
(a) The V bus, sub bus 11 and sub bus 12 each has termination circuits with two resistors of 120 Ohms.
5. 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 lines. If there is any trouble in the DLC3 or the DLC3 branch lines, ECUs on the CAN cannot output DTCs to the Techstream.
(b) Trouble in the CAN V bus (communication lines) can be checked by measuring the resistance between terminals of the DLC3. However, an open circuit in a branch line other than the DLC3 branch lines cannot be checked from the DLC3 (except branch line of the DLC3).
NOTICE:
Do not insert the tester probes directly into the DLC3. Be sure to use service wires.
6. DIAGNOSTIC TROUBLE CODES FOR CAN COMMUNICATION SYSTEM
HINT
See Diagnosis System Diagnosis System.
7. HOW TO DISTINGUISH CONNECTOR OF CAN JUNCTION CONNECTOR
(a) In the CAN communication system, the shape of connectors connected to the CAN junction connector which has an earth terminal is the same. The connectors connected to the CAN junction connector can be distinguished by the colors of the bus lines and the connecting side of the junction connector.
HINT
See Terminals of ECU for bus line color or the shape of connecting surface CAN Communication System.