CAN Communication System (Diagnostics - Introduction): Overview Lexus CT I

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1. NOTICE FOR INITIALIZATION NOTE: When disconnecting the cable from the negative (-) auxiliary battery terminal, initialize the following systems after the cable is reconnected. System Name See Procedure Parking Assist Monitor System Refer to «INITIALIZATION»(ref-568589-S03492911652013072300000) Power Door Lock Control System
2. PRECAUTIONS FOR STEERING SYSTEM HANDLING Be careful when replacing parts. Incorrect replacement could affect the performance of the steering system and result in hazardous driving.
3. PRECAUTIONS FOR SRS AIRBAG SYSTEM HANDLING This vehicle is equipped with a Supplemental Restraint System (SRS) which includes parts such as airbags for the driver and front passenger. Failure to carry out service operations in the correct sequence could cause unexpected SRS deployment during servicing and may cause a serious accident. Before servicing (including removal or installation of parts, inspection or replacement), be sure to read precaution for SRS. Refer to «PRECAUTION»(ref-568761-S11231002242013072300000) .
4. BUS LINE REPAIR After repairing a bus line with solder, wrap the repaired part with electrical tape. NOTE: The CANL bus line and CANH bus line must be installed together at all times. When installing, make sure that these lines are twisted, because CAN bus lines are likely to be influenced by electrical noise if the bus lines are not twisted. The difference in length between the CANL bus line and CANH bus line should be 100 mm (3.937 in.) or less. Leave approximately 80 mm (3.150 in.) loose in the twisted wires around the connector. Do not use bypass wiring between connectors. TEXT IN ILLUSTRATION *a Bypass Wire NOTE: The ability of the twisted bus lines to resist interference will be lost if bypass wiring is used.
5. CONNECTOR HANDLING When checking resistance with a tester, insert the tester probes from the backside (harness side) of the connector. TEXT IN ILLUSTRATION *a Tester Probe Use service wires to check the connector if it is impossible to check continuity from the rear of the connector. TEXT IN ILLUSTRATION *a Service Wire
6. PRECAUTIONS FOR INSPECTING OR REPLACING CAN JUNCTION CONNECTOR If the CAN junction connector is removed from the vehicle for inspection or replacement, make sure to install the CAN junction connector and all wire harnesses to their original locations with tape and the clamps.

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1. V1 BUS
2. V2 BUS
3. POWER MANAGEMENT BUS
4. CAN MS BUS (w/ Seat Position Memory)

SYSTEM DESCRIPTION

1. 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. By pairing the CANH and CANL bus lines, 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 ohms which are necessary to enable communication.
2. DEFINITION OF TERMS Main bus line 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. Branch line The branch line is a wire harness which diverges from the main bus line to an ECU or sensor. Terminating resistors 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 V1 Bus ECM Skid control ECU (Brake booster with master cylinder assembly) Main body ECU (Multiplex network body ECU) Yaw rate and acceleration sensor Power steering ECU assembly Certification ECU (Smart key ECU assembly) Airbag sensor assembly Steering angle sensor (Spiral cable with sensor sub-assembly) Transmission control ECU assembly Power management control ECU Combination meter assembly Navigation ECU (Display and navigation module display)*1 Navigation ECU (Navigation computer sub-assembly)*2 V2 Bus Power management control ECU Driving support ECU assembly*3 Seat belt control ECU*4 Parking assist ECU*1 Clearance warning ECU assembly*5 Power Management Bus Power management control ECU ECM Skid control ECU (Brake booster with master cylinder assembly) Air conditioning amplifier assembly CAN MS Bus Main body ECU (Multiplex network body ECU) Position control ECU and switch assembly*6 Outer mirror control ECU assembly (Driver side)*6 Outer mirror control ECU assembly (Front passenger side)*6 HINT: *1: w/ Navigation system (for DVD) *2: w/ Navigation system (for HDD) *3: w/ Dynamic radar cruise control system *4: w/ Pre-collision system *5: w/ Intuitive parking assist system *6: w/ Seat position memory
4. CIRCUIT DESCRIPTION The V1 bus, V2 bus and power management bus each have termination circuits with two resistors of 120 ohms. High speed communication at 500 kbps is possible. The CAN MS bus each have termination circuits with two resistors of 120 ohms. High speed communication at 250 kbps is possible.
5. TROUBLESHOOTING REMARKS 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 network cannot output codes to the Techstream. 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 HINT: See Diagnosis System. Refer to «DIAGNOSIS SYSTEM»(ref-568746-S10222482722013072300000) .
7. 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 lines and the connecting side of the junction connector. HINT: See Terminals of ECU for bus line color or the shape of connecting surface. Refer to «TERMINALS OF ECU»(ref-568746-S25790451642013072300000) .