Networking: Overview Toyota Corolla X

SYSTEM DESCRIPTION

1. LIN COMMUNICATION SYSTEM DESCRIPTION The multiplex communication system (LIN) is used to control communication between the ECUs of the body system. If communication cannot be performed through the LIN because of an open in the communication lines or other reason, the master control ECU of the relevant system will output a DTC. For the communication system and the connected ECUs, refer to the table below. HINT: Each ECU has a fail safe function which activates to maintain the minimum performance of the system and protect the system. LIN Communication Certification System LIN COMMUNICATION CERTIFICATION SYSTEM REFERENCE ECU Master Control (LIN Communication DTC Output Function) Certification ECU (Smart Key ECU Assembly) o (with output function) Main Body ECU (Instrument Panel Junction Block) o (with output function) Steering Lock ECU (Steering Lock Actuator Assembly) x (no output function) ID Code Box (Immobilizer Code ECU) x (no output function)

DESCRIPTION

This DTC is output when there is an open, short or ECU communication malfunction between the main body ECU (instrument panel junction block) and certification ECU (smart key ECU assembly).

DTC DETECTION CONDITION AND TROUBLE AREA

Scheme 1

The certification ECU (smart key ECU assembly) monitors communication between all the ECUs connected to the certification ECU system LIN bus lines. When the certification ECU (smart key ECU assembly) detects an error in communication with all the ECUs connected to the certification ECU system LIN bus lines at a set interval and 3 times in a row, DTC B2785 will be output.

DTC DETECTION CONDITION AND TROUBLE AREA

Scheme 2

This DTC is output when LIN communication between the certification ECU (smart key ECU assembly) and the steering lock ECU (steering lock actuator assembly) stops for more than 10 seconds.

DTC DETECTION CONDITION AND TROUBLE AREA

Scheme 3

This DTC is output when LIN communication between the certification ECU (smart key ECU assembly) and the ID code box (immobilizer code ECU) stops for more than 10 seconds.

DTC DETECTION CONDITION AND TROUBLE AREA

Scheme 4

1. BRIEF 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. 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 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 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 For vehicles with the smart key system: The CAN communication system consists of the CAN No. 1 bus and MS bus, which are connected to each system through the main body ECU. The CAN No. 1 bus and MS bus each have terminus circuits with 120 ohms, x 2 of resistance. High speed communication at 500 kbps and 250 kbps is possible.
4. ECUS OR SENSORS WHICH COMMUNICATE THROUGH CAN COMMUNICATION SYSTEM Skid control ECU Yaw rate sensor (w/ VSC) Steering angle sensor (w/ VSC) Main body ECU Center airbag sensor assembly ECM Certification ECU (w/ Smart key system) Air conditioning amplifier Combination meter Power steering ECU
5. DIAGNOSTIC CODE FOR CAN COMMUNICATION SYSTEM DTCs for the CAN communication system are as follows: U0073, U0100*1, U0123*1, U0124*1, U0126*1, U0129, U0327*2, U1002*2 and B1499. *1: w/VSC *2: w/ Smart key 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 a 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 tester probes directly into the DLC3. Be sure to use service wires.

The main body ECU will store this DTC when no signals can be received from the certification ECU while the CAN MS main bus is normal.

DTC DETECTION CONDITION AND TROUBLE AREA

Scheme 5

1. The main body ECU will store this DTC when no signals can be received from the ECUs that have been memorized as those that are connected to the CAN MS bus.
2. When the main body ECU receives a response signal from the ECUs connected to the CAN MS bus, the main body ECU recognizes and memorizes that the ECU is connected to the CAN MS bus. Based on this memorized data, the main body ECU monitors for malfunctions in the ECUs connected to the CAN MS bus when communicating with those ECUs. If the main body ECU cannot receive response signals from the ECUs that have been memorized as those connected to the CAN MS bus, the main body ECU determines that a malfunction exists.

DTC DETECTION CONDITION AND TROUBLE AREA

Scheme 6

SYMPTOM CHART

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SYMPTOM CHART

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Scheme 9

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SYMPTOM CHART

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SYMPTOM CHART

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SYMPTOM CHART

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SYMPTOM CHART

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SYMPTOM CHART

Scheme 17

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.

SYMPTOM CHART

Scheme 18

If any DTCs from the CAN communication system are not 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 wire, and +B or GND.

Scheme 19

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 ft.

SYMPTOM CHART

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Scheme 21

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.

SYMPTOM CHART

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.

SYMPTOM CHART

If some ECUs and sensors are not displayed the "CAN Bus Check" on 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 the "CAN Bus Check" from 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).

SYMPTOM CHART

See also:
• REGISTRATION
• REMOVAL
• AIR CONDITIONING AMPLIFIER
• ECM POWER SOURCE CIRCUIT
• ECM POWER SOURCE CIRCUIT