CAN Communication (Diagnostics): Overview Scion xD I

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1. PRECAUTION Turn the ignition switch off before measuring the resistances of the CAN main wire and the CAN branch wire. After the ignition switch is turned off, check that the key reminder warning system and light reminder warning system are not in operation. Before measuring the resistance, leave the vehicle as is for at least 1 minute and do not operate the ignition switch, any other switches or the doors. If doors need to be opened in order to check connectors, open the doors and leave them open. HINT: Operating the ignition switch, any switches or any doors triggers related ECU and sensor communication with the CAN, which causes resistance variation.
2. STEERING SYSTEM HANDLING PRECAUTIONS Care must be taken when replacing parts. Incorrect replacement could affect the performance of the steering system and result in hazards when driving.
3. SRS AIRBAG SYSTEM HANDLING PRECAUTIONS This vehicle is equipped with an SRS (Supplemental Restraint System) 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 Supplemental Restraint System. Refer to «PRECAUTION»(ref-388787-S38278378862011031100000).
4. BUS LINE REPAIR After repairing the bus line with solder, wrap the repaired part with vinyl tape. Refer to «ELECTRONIC CIRCUIT INSPECTION PROCEDURE»(ref-388639-S24992445372011031100000). NOTE: The CANL bus line and CANH bus line must be installed together. When installing, twist them together. CAN bus lines are likely to be influenced by noise if the bus lines are not twisted together. The difference in length between the CANL bus line and CANH bus line should be less than 100 mm (3.937 in.). Leave approximately 80 mm (3.150 in.) loose in the twisted wires around the connectors. Do not use bypass wiring between the connectors. NOTE: The feature of the twisted wire harness will be lost if bypass wiring is used.
5. CONNECTOR HANDLING When inserting tester probes into a connector, insert them from the rear of the connector. Use a repair wire to check the connector if it is impossible to check resistance from the rear of the connector.

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HINT

1. The ABS and traction actuator (skid control ECU) detects and stores steering sensor and yaw rate sensor DTCs and performs DTC communication by receiving information from the steering sensor and yaw rate sensor.
2. The center airbag sensor assembly use the conventional communication line (SIL) to perform DTC communication.

SYSTEM DESCRIPTION

1. BRIEF DESCRIPTION The CAN (Controller 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 (500 kbps) and the ability to detect malfunctions. By pairing the CANH and CANL bus lines, the CAN performs communication based on differential voltages. Many ECUs (sensors) installed on the vehicle operate by sharing information and communicating with each other. The CAN has two 120 ohms resistors which are necessary to communicate with the main wire.
2. DEFINITION OF TERMS Main wire The main wire is a wire harness between the two terminus circuits on the bus (communication line). This is the main bus in the CAN communication system. Branch wire A branch wire is a wire harness which diverges from the main wire to an ECU or sensor. Terminus circuit A terminus circuit is a circuit which converts the communication current of the CAN communication into the bus voltage. It consists of a resistor and condenser. Two terminus circuits are necessary on a bus. CAN junction connector A CAN junction connector is a junction designed for CAN communication.
3. ECUS OR SENSORS WHICH COMMUNICATE VIA CAN COMMUNICATION SYSTEM ABS and brake actuator (Skid control ECU) Power steering ECU Steering sensor Yaw rate sensor ECM Center airbag sensor assembly Air conditioning amplifier Combination meter ECU Main body ECU
4. DIAGNOSTIC CODES FOR CAN COMMUNICATION SYSTEM DTCs for the CAN communication system are as follows: U0073, U0100, U0123, U0124, U0126, U0129 and B1499.
5. NOTES REGARDING TROUBLESHOOTING Trouble in the CAN bus (communication line) can be checked through the DLC3 (except when there is a wire break other than in the branch wire of the DLC3). NOTE: Do not connect the tester directly to the DLC3 connector. Be sure to use a service wire. DTCs relating to the CAN communication system can be checked using a Techstream. The CAN communication system cannot detect trouble in the DLC3 branch line even though the DLC3 is also connected to the CAN communication system.

DESCRIPTION

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When any DTC for the CAN communication system is output, first measure the resistance between the terminals of the DLC3 to specify the trouble area, and check that there is no short in the CAN main wire, between the CAN bus lines, to +B, or to GND.

There may be an open circuit in the main wire and/or the DLC3 branch wire when the resistance between terminals 6 (CANH) and 14 (CANL) of the DLC3 is 69ohms or higher.

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There may 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.

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 no resistance exists between terminals 6 (CANH) and 4 (CG) or terminals 14 (CANL) and 4 (CG) of the DLC3.

If 2 or more ECUs and/or sensors do not appear on the Techstream "CAN Bus Check" screen, one side of the CAN branch wire may be open. (one side of the CAN-H [branch wire] / CAN-L [branch wire] of the ECU and/or sensor is open.)

See also:
• REMOVAL