LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lexus >> 2021 >> RC F Base >> Repair and Diagnosis >> Restraints >> Restraints Control Systems >> Pre-Collision System - Diagnostic Codes (2 Of 2) & Circuit Tests >> Pre-Collision System >> DTC U1104: Lost Communication with Driving Support ECU [11/2017 - 03/2019] >> Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC U1104: Lost Communication with Driving Support ECU [11/2017 - 03/2019]: Procedure

  1. CHECK FOR DTCs (PRE-COLLISION SYSTEM) 
    1. Check for DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Trouble Codes 

      Result

      Result Proceed to
      DTC U1104 and other DTCs are output A
      Only DTC U1104 is output B

    Result: 

    A 

    GO TO DIAGNOSTIC TROUBLE CODE CHART. Refer to  DIAGNOSTIC TROUBLE CODE CHART [11/2017 - 03/2019] 

    Result: 

    B 

    See step  2

  2. CHECK FOR DTCs (FORWARD RECOGNITION CAMERA SYSTEM) 
    1. Check for DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Chassis > Front Recognition Camera > Trouble Codes 

      Result

      Result Proceed to
      Forward recognition camera system DTCs are not output A
      Forward recognition camera system DTCs are output B

    Result: 

    B 

    GO TO FORWARD RECOGNITION CAMERA SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [11/2017 - 01/2023] 

    Result: 

    A 

    See step  3

  3. CHECK FOR DTCs (VEHICLE STABILITY CONTROL SYSTEM) 
    1. Check for DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 03/2019]

      Chassis > ABS/VSC/TRAC > Trouble Codes 

      Result

      Result Proceed to
      Vehicle stability control system DTC are not output A
      Vehicle stability control system DTC are output B

    Result: 

    B 

    GO TO VEHICLE STABILITY CONTROL SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [11/2017 - 03/2019] 

    Result: 

    A 

    See step  4

  4. TEST MODE INSPECTION (VEHICLE STABILITY CONTROL SYSTEM) 

    HINT: 

    When entering test mode, the skid control ECU (brake actuator assembly) communicates with the driving support ECU assembly to judge whether the vehicle is equipped with the pre-collision system. Therefore, do not exit test mode within 5 seconds of entering test mode.

    1. Procedure to enter Test Mode
      1. Turn the engine switch off.
      2. Check that the steering wheel is centered.
      3. Check that the shift lever is in P.
      4. Connect the Techstream to the DLC3.
      5. Turn the engine switch on (IG).
      6. Turn the Techstream on.
      7. Switch the skid control ECU (brake actuator assembly) to Test Mode (Signal Check) using the Techstream. Enter the following menus: Chassis / ABS/VSC/TRAC / Utility / Signal Check.

        HINT: 

        Do not exit Test Mode (Signal Check) within 5 seconds of entering Test Mode (Signal Check). If Test Mode (Signal Check) is exited within 5 seconds of entering Test Mode (Signal Check), DTC U1104 may be stored. If DTC U1104 is output after exiting Test Mode (Signal Check), enter Test Mode (Signal Check) again, wait at least 5 seconds, then recheck for DTCs.

        Chassis > ABS/VSC/TRAC > Utility 

        Tester Display
        Signal Check
      8. Check that the ABS warning and slip indicator lights come on for several seconds and then blink in the Test Mode pattern.

        HINT: 

        If the ABS warning and slip indicator lights do not blink, inspect the ABS warning and slip indicator light circuits.

    2. End of Test Mode (Signal Check)
      1. End Test Mode (signal check) using the Techstream
        1. Turn the engine switch off and enter normal mode.
        2. Remove the Techstream.

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  5

  5. CHECK FOR DTCs (PRE-COLLISION SYSTEM) 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Clear DTCs 

    2. Perform the following procedure.

      HINT: 

      If the following procedure is not performed, the previously output DTC cannot be detected.

      1. Turn the engine switch on (IG) and wait 1.5 seconds or more.
    3. Check for DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Trouble Codes 

      Result

      Result Proceed to
      DTC U1104 is not output A
      DTC U1104 is output B

    Result: 

    A 

    END 

    Result: 

    B 

    See step  6

  6. REPLACE MILLIMETER WAVE RADAR SENSOR ASSEMBLY 
    1. Replace the millimeter wave radar sensor assembly.

      Refer to REMOVAL [11/2017 - 01/2023]

    2. Adjust the millimeter wave radar sensor assembly.

      Refer to ADJUSTMENT [11/2017 - 03/2019]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  7

  7. CHECK FOR DTCs (PRE-COLLISION SYSTEM) 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Clear DTCs 

    2. Perform the following procedure.

      HINT: 

      If the following procedure is not performed, the previously output DTC cannot be detected.

      1. Turn the engine switch on (IG) and wait 1.5 seconds or more.
    3. Check for DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Trouble Codes 

      Result

      Result Proceed to
      DTC U1104 is not output A
      DTC U1104 is output B

    Result: 

    A 

    END (MILLIMETER WAVE RADAR SENSOR ASSEMBLY WAS DEFECTIVE) 

    Result: 

    B 

    See step  8

  8. REPLACE DRIVING SUPPORT ECU ASSEMBLY 
    1. Replace the driving support ECU assembly.

      Refer to REMOVAL [09/2014 - 01/2023]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  9

  9. CHECK FOR DTCs (PRE-COLLISION SYSTEM) 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Clear DTCs 

    2. Perform the following procedure.

      HINT: 

      If the following procedure is not performed, the previously output DTC cannot be detected.

      1. Turn the engine switch on (IG) and wait 1.5 seconds or more.
    3. Check for DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Trouble Codes 

      Result

      Result Proceed to
      DTC U1104 is not output A
      DTC U1104 is output B

    Result: 

    A 

    END (DRIVING SUPPORT ECU ASSEMBLY WAS DEFECTIVE) 

    Result: 

    B 

    See step  10

  10. REPLACE FORWARD RECOGNITION CAMERA 
    1. Replace the forward recognition camera.

      Refer to REMOVAL [11/2017 - 01/2023]

    2. Perform forward recognition camera adjustment.

      Refer to ADJUSTMENT (SEQUENTIAL RECOGNITION) [11/2017 - 01/2023]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  11

  11. CHECK FOR DTCs (PRE-COLLISION SYSTEM) 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Clear DTCs 

    2. Perform the following procedure.

      HINT: 

      If the following procedure is not performed, the previously output DTC cannot be detected.

      1. Turn the engine switch on (IG) and wait 1.5 seconds or more.
    3. Check for DTCs.

      Refer to DTC CHECK / CLEAR [11/2017 - 01/2023]

      Body Electrical > Pre-Collision 2 > Trouble Codes 

      Result

      Result Proceed to
      DTC U1104 is not output A
      DTC U1104 is output B

    Result: 

    A 

    END (FORWARD RECOGNITION CAMERA WAS DEFECTIVE) 

    Result: 

    B 

    See step  12

  12. REPLACE SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) 
    1. Replace the skid control ECU (brake actuator assembly).

      Refer to REMOVAL [11/2017 - 01/2023]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    END (SKID CONTROL ECU WAS DEFECTIVE) 

scientia non olet · About LEMON Manuals