Can Communication System (For Lhd) System Description

The CAN (Control 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.

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" . It operates at speeds of approximately 500 kbps. Terminating resistors for the CAN No. 1 bus are located in the combination meter and ECM. 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 MS-CAN bus are located in the main body ECU and the CAN J/C No. 3 (*1) or Certification ECU (*2). 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), which acts as a gateway.
*1: w/ TOYOTA Parking assist-sensor system
*2: w/o TOYOTA Parking assist-sensor system

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

Many ECUs (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 enable communication on the main bus wire.

Main bus wire

1. The main bus wire is a wire harness between the two terminus circuits on the bus (communication line).
   

Branch wire

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

Terminating resistors

1. Two resistors of 120 Ω resistance 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, a measurement of resistance between the two CAN bus lines should produce a reading of approximately 60 Ω.
   

CAN No. 1 Bus

1. ECM
   

2. Combination meter
   

3. Main body ECU
   

4. Skid control ECU with actuator
   

5. Yaw rate sensor*1
   

6. Steering angle sensor*1
   

7. Air conditioning amplifier
   

8. Center airbag sensor
   

9. Navigation receiver assembly*2
   

CAN MS Bus

1. Certification ECU*3
   

2. Clearance warning ECU*4
   

   HINT:

   *1: w/ VSC

   *2: w/ Navigation system

   *3: w/ Entry and start system

   *4: w/ TOYOTA Parking assist-sensor system

DTCs for the CAN communication system are as follows: U0073, U0100, U0101, U0123, U0124, U0126, U0129, B1499, B1207, B1297 and B2326.

DTCs for the CAN communication system can be checked using the intelligent tester via the CAN VIM. 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 via the CAN VIM.

Trouble in the CAN buses (communication lines) 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.

NOTICE:

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

In the CAN communication system, the shape of all connectors connected to the No. 1 CAN J/C is the same. The connectors connected to the No. 1 CAN J/C can be distinguished by the colors of the bus line and the connecting side of the junction connector.

HINT:

See "TERMINALS OF ECU" (CAMRY_ACV40 RM000000XVK053X.html) for bus line color or the type of connecting surface.