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 [03/2019 - 01/2023] >> Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC U1104: Lost Communication with Driving Support ECU [03/2019 - 01/2023]: 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 [03/2019 - 01/2023] 

    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 [03/2019 - 01/2023]

      Chassis > Brake > 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 [03/2019 - 01/2023] 

    Result: 

    A 

    See step  4

  4. PERFORM DEALER MODE (SIGNAL CHECK) (VEHICLE STABILITY CONTROL SYSTEM) 

    HINT: 

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

    1. Procedure to enter Dealer Mode (Signal Check).
      1. Turn the engine switch off.
      2. Apply the parking brake.
      3. Check that the shift lever is in P.
      4. Connect the Techstream to the DLC3.
      5. Turn the engine switch on (IG).
      6. Check that the steering wheel is centered.
      7. Turn the Techstream on.
      8. Enter the following menus: Chassis / Brake / Utility / Signal Check.

        Chassis > Brake > Utility 

        Tester Display
        Signal Check

        HINT: 

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

    2. Confirm the system has entered Dealer Mode (Signal Check)
      1. Confirm that the ABS warning light and slip indicator light indicate the Dealer Mode pattern (blinking at 0.25 seconds intervals).

        HINT: 

        If the ABS warning light or slip indicator light remains illuminated or does not illuminate when Dealer Mode (Signal Check) is entered, a component or wire harness may be malfunctioning.

    3. End of Dealer Mode (Signal Check)
      1. Turn the engine switch off and enter normal mode.
      2. Disconnect 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 [03/2019 - 01/2023]

      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