CAN COMMUNICATION SYSTEM SYSTEM DESCRIPTION


  1. BRIEF DESCRIPTION


    1. 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.

    2. By pairing the CANH and CANL bus lines, the CAN performs communication based on differential voltage.

    3. Many ECUs or sensors installed on the vehicle operate by sharing information and communicating with each other.

    4. The CAN has two resistors of 120 Ω which are necessary to enable communication.

  2. DEFINITION OF TERMS


    1. Main bus line


      1. The main bus line is a wire harness between the two terminating resistors on the bus (communication wire). This is the main bus in the CAN communication system.

    2. Branch line


      1. The branch line is a wire harness which diverges from the main bus line to an ECU or sensor.

    3. Terminating resistors


      1. Two resistors of 120 Ω 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 Ω.

  3. ECUS OR SENSORS WHICH COMMUNICATE THROUGH CAN COMMUNICATION SYSTEM


    1. V1 Bus


      1. ECM

      2. Skid control ECU (Brake booster with master cylinder assembly)

      3. Main body ECU (Multiplex network body ECU)

      4. Yaw rate and acceleration sensor

      5. Power steering ECU assembly

      6. Certification ECU (Smart key ECU assembly)

      7. Airbag sensor assembly

      8. Steering angle sensor (Spiral cable with sensor sub-assembly)

      9. Transmission control ECU assembly

      10. Power management control ECU

      11. Combination meter assembly

      12. Navigation ECU (Display and navigation module display)*1

      13. Navigation ECU (Navigation computer sub-assembly)*2

    2. V2 Bus


      1. Power management control ECU

      2. Driving support ECU assembly*3

      3. Seat belt control ECU*4

      4. Parking assist ECU*1*2

      5. Clearance warning ECU assembly*5

    3. Power Management Bus


      1. Power management control ECU

      2. ECM

      3. Skid control ECU (Brake booster with master cylinder assembly)

      4. Air conditioning amplifier assembly

    4. CAN MS Bus


      1. Main body ECU (Multiplex network body ECU)

      2. Position control ECU and switch assembly*6

      3. Outer mirror control ECU assembly (Driver side)*6

      4. Outer mirror control ECU assembly (Front passenger side)*6

        Tech Tips

        *1: w/ Navigation system (for DVD)

        *2: w/ Navigation system (for HDD)

        *3: w/ Dynamic radar cruise control system

        *4: w/ Pre-crash safety system

        *5: w/ LEXUS parking assist sensor system

        *6: w/ Seat position memory

  4. CIRCUIT DESCRIPTION


    1. The V1 bus, V2 bus and power management bus each have termination circuits with two resistors of 120 Ω. High speed communication at 500 kbps is possible.

    2. The CAN MS bus each have termination circuits with two resistors of 120 Ω. High speed communication at 250 kbps is possible.

  5. TROUBLESHOOTING REMARKS


    1. DTCs for the CAN communication system can be checked using the intelligent tester. 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 network cannot output codes to the intelligent tester.

    2. Trouble in the CAN V1 bus (communication wires) 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.

      Note

      Do not insert the tester probes directly into the DLC3. Be sure to use service wires.

  6. DIAGNOSTIC TROUBLE CODES FOR CAN COMMUNICATION SYSTEM

    Tech Tips

    See Diagnosis System Click here.

  7. HOW TO DISTINGUISH CONNECTOR OF CAN JUNCTION CONNECTOR


    1. 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.

      Tech Tips

      See Terminals of ECU for bus line color or the shape of connecting surface Click here.