CAN Communication System (Diagnostics & Symptom Tests): Overview Toyota Matrix E140

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1. DISCONNECT CABLE FROM NEGATIVE BATTERY TERMINAL WARNING: Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system. Be careful when replacing parts. Incorrect replacement could affect the performance of the steering system and result in hazardous driving.
2. STEERING SYSTEM HANDLING PRECAUTIONS Be careful when replacing parts. Incorrect replacement could affect the performance of the steering system and result in hazardous driving.
3. SRS AIRBAG SYSTEM HANDLING PRECAUTIONS This vehicle is equipped with a Supplemental Restraint System (SRS) which includes parts such as the driver airbag and front passenger airbag. Failure to carry out service operations in the correct sequence could cause unexpected SRS deployment during servicing and may lead to a serious accident. Before servicing (including removal or installation of parts, inspection or replacement), be sure to read the precautionary notice for the SRS. Refer to «PRECAUTION»(ref-427508-S03121118652011101200000).
4. BUS WIRE REPAIR After repairing a bus wire with solder, wrap the repaired part with electrical tape. NOTE: The CANL bus wire and CANH bus wire must be installed together at all times. When installing, make sure that the wires are twisted. CAN bus wires are likely to be influenced by electrical noise if they are not twisted. The difference in length between the CANL bus wire and CANH bus wire 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 the connectors. NOTE: The ability of the twisted bus wires 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. Use service wires to check the connector if it is impossible to check continuity from the rear of the connector.
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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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 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 ohms which are necessary to communicate with the main bus wire.
2. DEFINITION OF TERMS Main bus wire The main bus wire is a wire harness between the 2 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 ohms are installed in parallel across the ends of the CAN 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 ohms.
3. CIRCUIT DESCRIPTION The CAN No. 1 bus has 2 terminating resistors of 120 ohms. High speed communication at 500 kbps is possible.
4. ECUS OR SENSORS WHICH COMMUNICATE USING CAN COMMUNICATION SYSTEM Skid control ECU Yaw rate sensor Steering angle sensor Main body ECU Center airbag sensor assembly ECM Air conditioning amplifier (w/ air conditioning system) Combination meter Power steering ECU 4WD control ECU (for 4WD) Accessory gateway
5. DIAGNOSTIC CODE FOR CAN COMMUNICATION SYSTEM DTCs for the CAN communication system are as follows: U0073, U0100, U0123, U0124, U0126, U0129 and B1499*1. *1: w/ Air conditioning system
6. 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 wires. If there is trouble in the DLC3 or the DLC3 branch wires, ECUs on the CAN network cannot output codes to the Techstream. 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. NOTE: Do not insert the Techstream probes directly into the DLC3. Be sure to use service wires.

DESCRIPTION

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There may be an open circuit in the CAN main wire and/or the DLC3 branch wire when the resistance between terminals 6 (CANH) and 14 (CANL) of the DLC3 is 70 ohms or higher.

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There may be a short circuit in the CAN main wire and/or CAN branch wire when the resistance between terminals 6 (CANH) and 14 (CANL) of the DLC3 is below 54 ohms.

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There may be a short circuit between the CAN bus line and +B when no resistance exists between terminals 6 (CANH) and 16 (BAT) or terminals 14 (CANL) and 16 (BAT) of the DLC3.

There may be a short circuit between the CAN bus line and GND when there is no resistance between terminals 6 (CANH) and 4 (CG) or terminals 14 (CANL) and 4 (CG) of the DLC3.

If some ECUs and sensors are not displayed on the "CAN Bus Check" screen of the Techstream and some ECUs and sensors repeatedly appear and disappear from the screen when the CAN main bus wires are normal (there is no open, short, short to B+, or short to GND in the main bus wires), there may be an open circuit in either of the CAN branch wires.

HINT

If some ECUs and sensors repeatedly appear and disappear from the "CAN Bus Check" screen, communication between the normal ECUs (sensors) and the Techstream may be affected by the incomplete signals that are output from the ECU that has an open circuit in either of its CAN branch wires. In this case, the CAN branch wires for the ECUs and sensors that repeatedly appear and disappear from the screen are normal and the ECU that is not displayed on the screen may be the main cause of the problem (this ECU may have an open circuit in either of its CAN branch wires).

See also:
• REMOVAL
• REMOVAL