BRIEF DESCRIPTION
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.
Two different types of CAN buses are used. The CAN buses are classified into two types based on typical communication speed.
The HS-CAN bus is a high speed communication bus that is used for powertrain, chassis and some body electrical communication. The HS-CAN bus is referred to as "CAN No. 1 bus", "CAN No. 2 bus", "power management bus" or "sensor bus" and it operates at speeds of approximately 500 kbps. Terminating resistors for the CAN No. 1 bus are located in the certification ECU and ECM. Terminating resistors for the CAN No. 2 bus are located in the power management control ECU and CAN No. 5 junction connector. Terminating resistors for the power management bus are located in the power management control ECU and ECM. Terminating resistors for the sensor bus are located in the driving support ECU assembly and millimeter wave radar sensor assembly. The resistance of the CAN No. 2 bus, power management bus, and sensor bus cannot be measured from the DLC3 connector.
The MS-CAN bus is a medium speed communication bus that is used for body electrical communication. The MS-CAN bus is referred to as "CAN MS bus" and it operates at speeds of approximately 250 kbps. Terminating resistors for the CAN MS bus are located in the main body ECU and tilt and telescopic ECU. The resistance of the CAN MS bus cannot be measured from the DLC3 connector.
Communication between these networks is handled via the main body ECU (for the CAN MS bus) or the power management control ECU (for the CAN No. 2 bus and power management bus), which acts as a gateway.
By pairing the CANH and CANL bus wires, the CAN performs communication based on differential voltage.
Many ECUs or sensors installed on the vehicle operate by sharing information and communicating with each other.
The CAN has two resistors of 120 Ω which are necessary to communicate with the main bus wire.
DEFINITION OF TERMS
Main bus wire
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.
Branch wire
The branch wire is a wire harness which diverges from the main bus wire to an ECU or sensor.
Terminating resistors
Two resistors of 120 Ω are installed in parallel across the ends of the 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 Ω.
ECUS OR SENSORS WHICH COMMUNICATE THROUGH CAN COMMUNICATION SYSTEM
CAN No. 1 Bus
ECM
Main body ECU (Multiplex network body ECU)
Combination meter
Power steering ECU
Center airbag sensor assembly
Skid control ECU (Brake actuator assembly)
Steering angle sensor
Yaw rate sensor
Certification ECU (Smart key ECU)
Power management control ECU
Multi-media module receiver assembly*1
Radio receiver assembly*2
CAN No. 2 Bus
Power management control ECU
AFS ECU (Headlight swivel ECU)*3*4
4WD control ECU*5
Suspension control ECU*6
Driving support ECU assembly*7
Seat belt control ECU*8
Parking assist ECU*9
Clearance warning ECU*10
CAN MS Bus
Main body ECU (Multiplex network body ECU)
Tilt and telescopic ECU (Multiplex tilt and telescopic ECU)
Outer mirror control ECU RH*11
Outer mirror control ECU LH*11
Position control ECU RH*11
Position control ECU LH*11
Power back door ECU (Back door motor unit)*12
Power Management Bus
Air conditioning amplifier
Sensor Bus*7
Driving support ECU assembly
Millimeter wave radar sensor assembly
*1: w/ Navigation system
*2: w/ Audio and visual system (w/ Multi-display)
*3: w/ Automatic headlight beam level control system
*4: w/ AFS (Adaptive front-lighting system)
*5: for AWD
*6: w/ Air suspension system
*7: w/ Dynamic radar cruise control system
*8: w/ Pre-crash safety system
*9: w/ Parking assist monitor system (w/ side monitor system)
*10: w/ LEXUS parking assist-sensor system (w/o side monitor system)
*11: w/ Position memory system
*12: w/ Power back door system
DIAGNOSTIC TROUBLE CODE FOR CAN COMMUNICATION SYSTEM
DTCs for the CAN communication system are as follows: U0073, U0100, U0101, U0104, U0114, U0122, U0123, U0124, U0126, U0129, U0130, U0131, U0132, U0140, U0142, U0151, U0155, U0163, U0164, U0182, U0199, U0200, U0208, U0209, U0230, U0235, U0327, U1000, U1002, U1100, U1101, U1102, U1104, U110B, U1110, U1115, U1121, U1126 and U1133.
TROUBLESHOOTING REMARKS
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 wires. If there is trouble in the DLC3 or the DLC3 branch wires, ECUs on the CAN network cannot output codes to the intelligent tester.
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.
Do not insert the tester probes directly into the DLC3. Be sure to use service wires.
HOW TO DISTINGUISH CONNECTOR OF CAN JUNCTION CONNECTOR
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 wire and the connecting side of the junction connector.
See Terminals of ECU for bus wire color or the shape of connecting surface (Click here).