CAN COMMUNICATION SYSTEM SYSTEM DESCRIPTION

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. 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.)
3. Many ECUs or sensors installed to the vehicle operate by sharing information and communicating with each other.
4. The V bus has termination circuits with a resistor of 60 Ω, and the bus 2, bus 3, bus 4, bus 5 and sub bus 1 each have termination circuits with two resistors of 120 Ω.
DEFINITION OF TERMS
1. 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.
2. Branch
  1. A branch is a wire harness which diverges from the main bus 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.
ECUS OR SENSORS WHICH COMMUNICATE THROUGH CAN COMMUNICATION SYSTEM
1. Bus 2
  1. Central gateway ECU (network gateway ECU)
  2. ECM
  3. Skid control ECU (brake actuator assembly)
  4. Headlight leveling ECU assembly*1
  5. Steering sensor
  6. Main body ECU (multiplex network body ECU)
  7. Airbag ECU assembly
  8. Yaw rate sensor
  9. Front steering control ECU*2
  10. Power steering ECU assembly
  11. Certification ECU (smart key ECU assembly)
  12. Air conditioning amplifier assembly
  13. Stereo component equalizer assembly*3
  14. Combination meter assembly
  15. Engine stop and start ECU*4
2. Bus 3
  1. Central gateway ECU (network gateway ECU)
  2. Radio receiver assembly
  3. Telematics transceiver*5
  4. Option connector (bus buffer ECU)*6
3. Bus 4*2
  1. Central gateway ECU (network gateway ECU)
  2. Skid control ECU (brake actuator assembly)
  3. Driving support ECU assembly*7
  4. Absorber control ECU
  5. Front steering control ECU
  6. Power steering ECU assembly
  7. Rear steering control ECU
4. Bus 5
  1. Central gateway ECU (network gateway ECU)
  2. Driving support ECU assembly*7
  3. Absorber control ECU*8
  4. Forward recognition camera*7
  5. Millimeter wave radar sensor assembly*7
  6. Clearance warning ECU assembly*9
  7. Blind spot monitor sensor LH*10
  8. Rear television camera assembly*11
5. Sub Bus 1
  1. Main body ECU (multiplex network body ECU)
  2. Multiplex tilt and telescopic ECU*12
  3. Headlight light control ECU sub-assembly LH*13
  4. Outer mirror control ECU assembly (for driver side)*14
  5. Outer mirror control ECU assembly (for front passenger side)*14
  6. Position control ECU and switch assembly LH
  7. Position control ECU and switch assembly RH
Tech Tips

*1: for Single Beam Headlight

*2: w/ VGRS System

*3: w/ ASC System

*4: w/ Stop and Start System

*5: w/ Telematics Transceiver

*6: w/ CAN Compatible Optional Devices

*7: w/ Lexus Safety System +

*8: w/ AVS System

*9: w/ LEXUS Parking Assist-sensor System

*10: w/ Blind Spot Monitor System

*11: w/ Parking Assist Monitor System

*12: w/ Power Tilt and Power Telescopic System

*13: for Triple Beam Headlight

*14: w/ Seat Position Memory System
CIRCUIT DESCRIPTION
1. The V bus has a termination circuit with a resistor of 60 Ω.
2. The bus 2, bus 3, bus 4, bus 5 and sub bus 1 each have termination circuits with two resistors of 120 Ω.
TROUBLESHOOTING REMARKS
1. DTCs for the CAN communication system can be checked using the GTS. 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 a malfunction in the DLC3 or the DLC3 branch lines, ECUs on the CAN cannot output DTCs to the GTS.
DIAGNOSTIC TROUBLE CODES FOR CAN COMMUNICATION SYSTEM

Tech Tips

See Diagnosis System.

Click here
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 are 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 connectors.
  
  Click here