CAN Communication System (Diagnostics & Symptom Tests): Overview Lexus IS II facelift 2

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1. PRECAUTION FOR DISCONNECTING CABLE FROM NEGATIVE BATTERY TERMINAL NOTE: When disconnecting the cable from the negative (-) battery terminal, initialize the following systems after the cable is reconnected. System Name See Procedure Parking Assist Monitor System Refer to «INITIALIZATION [08/2012 - ]»(ref-606329-S33601054862014032500000)
2. CAN COMMUNICATION SYSTEM TROUBLESHOOTING Because the order of diagnosis is important to allow correct diagnosis, make sure to begin troubleshooting using How to Proceed with Troubleshooting when CAN communication system related DTCs are output. Refer to «HOW TO PROCEED WITH TROUBLESHOOTING [08/2012 - ]»(ref-606524-S11885193892014032500000).
3. STEERING SYSTEM HANDLING PRECAUTIONS Care must be taken when replacing parts. Incorrect replacement could affect the performance of the steering system and result in hazardous driving.
4. SRS AIRBAG SYSTEM HANDLING PRECAUTIONS This vehicle is equipped with an Supplemental Restraint System (SRS) which includes components 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 [08/2012 - ]»(ref-606516-S09770350952014032500000).
5. BUS LINE REPAIR After repairing the bus line with solder, wrap the repaired part with electrical tape. NOTE: The CANL bus line and CANH bus line must be installed together all the times. When installing, make sure to twist them. CAN bus lines are likely to be influenced by electrical noise if they 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 the connectors. NOTE: The ability of the twisted bus lines to resist interference will be lost if bypass wiring is used.
6. 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.

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HINT

1. The skid control ECU detects and stores steering angle sensor and yaw rate sensor DTCs, and performs DTC communication by receiving information from the steering angle sensor and yaw rate sensor.
2. The CAN communication system connects to other networks via ECUs that function as a gateway. Refer to «SYSTEM DIAGRAM [08/2012 - ]»(ref-606519-S36669408072014032500000).

SYSTEM DESCRIPTION [08/2012 - ]

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 (500 kbps) and the ability to detect malfunctions. CAN communication is performed using the voltage differential between the CANH and CANL bus lines. To produce a "1", the voltage on the CANH bus line rises high at the same time as the voltage on the CANL bus line drops low. This creates a voltage difference between the two lines. A "1" is judged when a specified voltage differential exists. (A signal is a combination of the base voltage applied to both lines and an opposite signal voltage that is sent to each bus line.) 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 line.
2. DEFINITION OF TERMS Main bus line The main bus line is a wire harness between the two terminating resistors on the bus (communication line). This is the main bus in the CAN communication system. Refer to «SYSTEM DIAGRAM [08/2012 - ]»(ref-606524-S34689882782014032500000). Branch line The branch line is a wire harness which diverges from the main bus line to an ECU or sensor. Refer to «SYSTEM DIAGRAM [08/2012 - ]»(ref-606524-S34689882782014032500000). Terminating resistors Two resistors of 120 ohms 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 ohms. Refer to «SYSTEM DIAGRAM [08/2012 - ]»(ref-606524-S34689882782014032500000).
3. ECUS OR SENSORS WHICH COMMUNICATE USING CAN COMMUNICATION SYSTEM Skid control ECU Yaw rate sensor Steering angle sensor Center airbag sensor ECM Gateway ECU Power steering ECU 4WD control ECU*1 Multi-media module receiver assembly*2*3 HINT: *1: for 4WD *2: w/ Navigation System *3: w/o Navigation System with Multi-display
4. DIAGNOSTIC CODE FOR CAN COMMUNICATION SYSTEM DTCs for the CAN communication system are as follows: U0073, U0100, U0101, U0105, U0121, U0123, U0124, U0126 and U0129.
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 trouble in the DLC3 or the DLC3 branch lines, ECUs on the CAN communication system output codes to the Techstream. Trouble in the CAN buse (communication lines) can be checked by measuring the resistance between terminals of the DLC3. However, an open circuit in a branch line cannot be checked from the DLC3 (except branch line of the DLC3). NOTE: Do not insert the tester probes directly into the DLC3. Be sure to use service wires.
6. HOW TO DISTINGUISH THE CAN J/C CONNECTOR In the CAN communication system, the shape of all connectors connected to the CAN J/C is the same. The connectors connected to the 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". Refer to «TERMINALS OF ECU [08/2012 - ]»(ref-606524-S31891749882014032500000) for bus line color or the type of connecting surface.

DESCRIPTION

HINT

"ABS/VSC/TRAC" refers to the circuit that includes the skid control ECU.

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HINT

"EPS" refers to the circuit that includes the power steering ECU.

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HINT

"Gateway" refers to the circuit that includes the gateway ECU.

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HINT

"Steering Angle Sensor" refers to the circuit that includes the steering angle sensor.

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HINT

"Yaw Rate / Deceleration Sensor" refers to the circuit that includes the yaw rate sensor.

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HINT

"Engine" and "ECT" refer to the circuit that includes the ECM.

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HINT

"SRS Airbag" refers to the circuit that includes the center airbag sensor.

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HINT

"Four Wheel Drive Control" refers to the circuit that includes the 4WD control ECU.

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HINT

"AVN1" refers to the circuit that includes the multi-media module receiver assembly.

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

This malfunction is not related to the lines of a CAN branch or to ECUs or sensors connected a CAN branch.

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The CAN bus lines are considered to be shorted when the resistance between terminals 6 (CANH) and 14 (CANL) of the DLC3 is below 54 ohms.

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A short to B+ is suspected in the CAN bus line when the resistance between terminals 6 (CANH) and 16 (BAT), or terminals 14 (CANL) and 16 (BAT) of the DLC3 is below 6 kohms.

A short to GND is suspected in the CAN bus line when the resistance between terminals 4 (CG) and 6 (CANH), or terminals 4 (CG) and 14 (CANL) of the DLC3 is below 200 ohms.

If there is an open in one of the CAN branch lines for an ECU or sensor connected to the CAN communication system, this may affect the ECUs and sensors with normal CAN branch lines, resulting in communication errors between normal ECUs and sensors.

See also:
• REMOVAL [08/2012 - ]