2013 Lexus IS 350C BaseFACTORY OEM SERVICE PROCEDURE

DTC U0073: Control Module Communication Bus OFF; DTC U0100: Lost Communication with ECM / PCM; DTC U0123: Lost Communication with Yaw Rate Sensor Module; DTC U0124: Lost Communication with Lateral Acceleration Sensor Module; DTC U0126: Lost Communication with Steering Angle Sensor Module: Procedure

  1. CHECK HARNESS AND CONNECTOR (MOMENTARY INTERRUPTION) 
    1. Using the Techstream, check for any momentary interruption in the wire harness and connector corresponding to the DTC. Refer to CHECK FOR INTERMITTENT PROBLEMS [08/2012 - ] .
      ABS/VSC/TRAC

      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      EFI Communication Open EFI communication open detection / ERROR or NORMAL ERROR: Momentary interruption
      NORMAL: Normal
      -
      Yaw Rate Open Yaw rate sensor open detection / ERROR or NORMAL ERROR: Momentary interruption
      NORMAL: Normal
      -
      Steering Open Steering angle sensor open detection / ERROR or NORMAL ERROR: Momentary interruption
      NORMAL: Normal
      -

      Result

      Result Proceed to
      There is a constant open circuit A
      There are no momentary interruptions B
      There are momentary interruptions C

      HINT: 

      Perform the above inspection before removing the sensor and connector.

    B → See step   3 

    C → See step   4 

    A: Go to next step 

  2. CHECK IF EACH SENSOR AND ECM CONNECTOR IS SECURELY CONNECTED 
    1. Turn the engine switch off.
    2. Check if each sensor and ECM connector is securely connected.

      OK

      Each connector is securely connected.

    NG → CONNECT CONNECTOR TO EACH SENSOR OR ECM CORRECTLY 

    OK: Go to next step 

  3. RECONFIRM DTC 
    1. Turn the engine switch off.
    2. Record the output DTCs (for ABS, VSC system and/or CAN communication system). Refer to DTC CHECK / CLEAR [08/2012 - ] for ABS and VSC system, or refer to DIAGNOSIS SYSTEM [08/2012 - ] for CAN communication system).

      HINT: 

      If CAN communication system DTCs and the relevant sensor DTCs are output simultaneously, troubleshoot the relevant sensor DTCs (for ABS and/or VSC system) after the CAN communication system returns to normal.

      Result

      Result Proceed to
      DTC is not output A
      DTC (ABS and/or VSC system DTC) is output B
      DTC (CAN communication system DTC) is output C

    B → See step   7 

    C → See step   6 

    A → See step   8 

  4. REPAIR OR REPLACE HARNESS OR CONNECTOR 
    1. Turn the engine switch off.
    2. Repair or replace the harness or connector.
    3. Check for any momentary interruption between the skid control ECU and each sensor or ECM. Refer to CHECK FOR INTERMITTENT PROBLEMS [08/2012 - ] .
    4. Check that there are no momentary interruptions.

    NEXT: Go to next step 

  5. RECONFIRM DTC 
    1. Turn the engine switch off.
    2. Clear the DTCs. Refer to DTC CHECK / CLEAR [08/2012 - ] .
    3. Start the engine.
    4. Drive the vehicle and turn the steering wheel to the right and left at a speed of 15 km/h (9 mph) or more.
    5. Check that no CAN communication system DTC is output. Refer to DIAGNOSIS SYSTEM [08/2012 - ] .
    6. If ABS and/or VSC system DTCs are output, record them.

      Result

      Result Proceed to
      DTC is not output A
      DTC (ABS and/or VSC system DTC) is output B
      DTC (CAN communication system DTC) is output C

      HINT: 

      The CAN communication system must be normal when performing troubleshooting for each sensor DTC (for ABS and/or VSC system).

    B → See step   7 

    C → See step   6 

    A → END 

  6. INSPECT CAN COMMUNICATION SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [08/2012 - ] 
  7. REPAIR CIRCUIT INDICATED BY OUTPUT DTC. Refer to  DIAGNOSTIC TROUBLE CODE CHART [08/2012 - ] 
  8. CHECK FOR INTERMITTENT PROBLEMS. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [08/2012 - ] 
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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