Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Open in One Side of Bus 5 Branch Line

DESCRIPTION

If an ECU or sensor is 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 lines are normal (there is no open, short, short to +B or short to GND in the main bus lines), there may be an open circuit in either of the lines in a CAN branch.

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 the lines in its CAN branch. In this case, the CAN branch lines 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 the lines in its CAN branch).

Symptom

Trouble Area

2 or more ECUs and/or sensors do not appear on the Techstream CAN Bus Check screen.

One side of CAN branch line is open, or output signals are incomplete.

  • Certification ECU (smart key ECU assembly)
  • Combination meter mirror ECU (headup display) (w/ Headup Display System)
  • Headlight ECU sub-assembly LH (w/ Automatic Headlight Beam Level Control System)
  • Air conditioning amplifier assembly
  • Main body ECU (multiplex network body ECU)

CAUTION / NOTICE / HINT

NOTICE:

  • 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.

    Click here

  • After performing repairs, perform the DTC check procedure and confirm that the DTCs are not output again.
  • After the repair, perform the CAN bus check and check that all the ECUs and sensors connected to the CAN communication system are displayed.

    Click here

  • DTC check procedure: Drive the vehicle at a speed of 5 km/h (3 mph) or more for 52 seconds or more.
  • Before replacing the certification ECU (smart key ECU assembly), refer to the smart access system with push-button start (for Start Function) Precaution.

    Click here

  • If the main body ECU (multiplex network body ECU) is replaced, refer to Registration.

    Click here

HINT:

Even after DTCs are cleared, if a DTC is stored again after driving the vehicle for a while, the malfunction may be occurring due to vibration of the vehicle. In such a case, wiggling the ECUs or wire harness while performing the inspection below may help determine the cause of the malfunction.

PROCEDURE

1.

CHECK FOR OPEN IN ONE SIDE OF BUS 5 BRANCH LINE

(a) Based on the vehicle equipment and specifications, confirm the systems that use CAN communication.

Click here

(b) Using the Techstream, select and perform the CAN bus check.

Click here

(c) Observe the screen for approximately 2 minutes to check the ECUs and sensors that are not displayed on the screen and also those that repeatedly appear and disappear from the screen.

(d) Check the applicable communication stop mode for the ECU or sensor that is not displayed on the screen.

NEXT

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