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Home >> Lexus >> 2019 >> RX 450h Base >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Exterior Lights >> Lighting System (W/ Automatic Headlight Beam Level Control System) (Diagnostic Codes) (2 Of 2) & Circuit Tests) >> Lighting System (W/ Automatic Headlight Beam Level Control System) >> DTC U0242: Lost Communication With Headlamp Control Module "B" [10/2015 - 08/2019] >> Procedure
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DTC U0242: Lost Communication With Headlamp Control Module "B" [10/2015 - 08/2019]: Procedure

  1. CONFIRM MODEL 
    1. Choose the model to be inspected.

      Result

      Result Proceed to
      for Single Beam Headlight without AFS (Adaptive Front-lighting System) A
      for Triple Beam Headlight, for Single Beam Headlight with AFS (Adaptive Front-lighting System) B

    Result: 

    B 

    See step  8

    Result: 

    A 

    See step  2

  2. CLEAR DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > HL AutoLeveling > Clear DTCs 

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  3

  3. CHECK FOR DTC 
    1. Turn the power switch on (IG).
    2. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > HL AutoLeveling > Trouble Codes 

      OK

      DTC U0242 is not output.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [10/2015 - 08/2016]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [08/2016 - 12/2017]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [12/2017 - 03/2018]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [03/2018 - 08/2019] 

    Result: 

    NG 

    See step  4

  4. CHECK HARNESS AND CONNECTOR (HEADLIGHT ECU SUB-ASSEMBLY LH - HEADLIGHT SUB-ASSEMBLY RH) 
    1. Disconnect the A49 headlight ECU sub-assembly LH connector.
    2. Disconnect the A50 headlight ECU sub-assembly RH connector.
    3. Measure the resistance according to the value (s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A49-20 (LINL) - A50-20 (LINL) Always Below 1 Ω
      A49-20 (LINL) or A50-20 (LINL) - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  5

  5. REPLACE HEADLIGHT ECU SUB-ASSEMBLY RH 
    1. Replace the headlight ECU sub-assembly RH with a new or known good one.

      Refer to REMOVAL [10/2015 - 08/2016] , or refer to REMOVAL [08/2016 - 08/2019]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  6

  6. CLEAR DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > HL AutoLeveling > Clear DTCs 

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  7

  7. CHECK FOR DTC 
    1. Turn the power switch on (IG).
    2. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > HL AutoLeveling > Trouble Codes 

      OK

      DTC U0242 is not output.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    END (HEADLIGHT ECU SUB-ASSEMBLY RH WAS DEFECTIVE) 

    Result: 

    NG 

    REPLACE HEADLIGHT ECU SUB-ASSEMBLY LH. Refer to  REMOVAL [10/2015 - 08/2016]  , or refer to  REMOVAL [08/2016 - 08/2019] 

  8. CLEAR DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Clear DTCs 

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  9

  9. CHECK FOR DTC 
    1. Turn the power switch on (IG).
    2. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Trouble Codes 

      OK

      DTC U0242 is not output.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [10/2015 - 08/2016]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [08/2016 - 12/2017]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [12/2017 - 03/2018]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [03/2018 - 08/2019] 

    Result: 

    NG 

    See step  10

  10. CHECK CAN BUS LINE (MALFUNCTION CONFIRMATION) 
    1. Turn the power switch off.
    2. Disconnect the cable from the negative (-) auxiliary battery terminal.
    3. Disconnect the A49 headlight ECU sub-assembly LH connector.
    4. Measure the resistance according to the value (s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition Result
      A49-21 (LCL) - A49-22 (LCH) Cable disconnected from negative (-) auxiliary battery terminal 108 to 132 Ω 132 Ω or more:
      Open circuit in main bus lines
      Below 108 Ω:
      Short circuit between bus lines
      A49-21 (LCL) - GND Cable disconnected from negative (-) auxiliary battery terminal 200 Ω or higher Below 200 Ω:
      LCL short to ground
      A49-22 (LCH) - GND Cable disconnected from negative (-) auxiliary battery terminal 200 Ω or higher Below 200 Ω:
      LCH short to ground
      A49-21 (LCL) - +B Cable disconnected from negative (-) auxiliary battery terminal 6 kΩ or higher Below 6 kΩ:
      LCL +B short
      A49-22 (LCH) - +B Cable disconnected from negative (-) auxiliary battery terminal 6 kΩ or higher Below 6 kΩ:
      LCH +B short

      Result

      Result Proceed to
      OK A
      NG (Open circuit in main lines) B
      NG (Short circuit between main lines) C
      NG (Short to +B or ground) D

    Result: 

    A 

    REPLACE HEADLIGHT ECU SUB-ASSEMBLY LH. Refer to  REMOVAL [10/2015 - 08/2016]  , or refer to  REMOVAL [08/2016 - 08/2019] 

    Result: 

    C 

    See step  15

    Result: 

    D 

    See step  19

    Result: 

    B 

    See step  11

  11. CHECK FOR OPEN IN CAN BUS MAIN LINES (HEADLIGHT ECU SUB-ASSEMBLY LH - HEADLIGHT ECU SUB-ASSEMBLY RH) 
    1. Connect the A49 headlight ECU sub-assembly LH connector.
    2. Disconnect the A50 headlight ECU sub-assembly RH connector.
    3. Measure the resistance according to the value (s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A50-21 (LCL) - A50-22 (LCH) Cable disconnected from negative (-) auxiliary battery terminal 108 to 132 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE CAN BUS MAIN LINE OR CONNECTOR 

    Result: 

    OK 

    See step  12

  12. REPLACE HEADLIGHT ECU SUB-ASSEMBLY RH 
    1. Replace the headlight ECU sub-assembly RH with a new or known good one.

      Refer to REMOVAL [10/2015 - 08/2016] , or refer to REMOVAL [08/2016 - 08/2019]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  13

  13. CLEAR DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Clear DTCs 

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  14

  14. CHECK FOR DTC 
    1. Turn the power switch on (IG).
    2. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Trouble Codes 

      OK

      DTC U0242 is not output.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    END (HEADLIGHT ECU SUB-ASSEMBLY RH WAS DEFECTIVE) 

    Result: 

    NG 

    REPLACE HEADLIGHT ECU SUB-ASSEMBLY LH. Refer to  REMOVAL [10/2015 - 08/2016]  , or refer to  REMOVAL [08/2016 - 08/2019] 

  15. CHECK FOR SHORT BETWEEN CAN BUS LINES (HEADLIGHT ECU SUB-ASSEMBLY LH - HEADLIGHT ECU SUB-ASSEMBLY RH) 
    1. Connect the A49 headlight ECU sub-assembly LH connector.
    2. Disconnect the A50 headlight ECU sub-assembly RH connector.
    3. Measure the resistance according to the value (s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A50-21 (LCL) - A50-22 (LCH) Cable disconnected from negative (-) auxiliary battery terminal 108 to 132 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE CAN BUS MAIN LINE OR CONNECTOR 

    Result: 

    OK 

    See step  16

  16. REPLACE HEADLIGHT ECU SUB-ASSEMBLY RH 
    1. Replace the headlight ECU sub-assembly RH with a new or known good one.

      Refer to REMOVAL [10/2015 - 08/2016] , or refer to REMOVAL [08/2016 - 08/2019]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  17

  17. CLEAR DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Clear DTCs 

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  18

  18. CHECK FOR DTC 
    1. Turn the power switch on (IG).
    2. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Trouble Codes 

      OK

      DTC U0242 is not output.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    END (HEADLIGHT ECU SUB-ASSEMBLY RH WAS DEFECTIVE) 

    Result: 

    NG 

    REPLACE HEADLIGHT ECU SUB-ASSEMBLY LH. Refer to  REMOVAL [10/2015 - 08/2016]  , or refer to  REMOVAL [08/2016 - 08/2019] 

  19. CHECK FOR FOR SHORT IN CAN BUS LINE (HEADLIGHT ECU SUB-ASSEMBLY LH - HEADLIGHT ECU SUB-ASSEMBLY RH) 
    1. Disconnect the A50 headlight ECU sub-assembly RH connector.
    2. Measure the resistance according to the value (s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A50-21 (LCL) - GND Cable disconnected from negative (-) auxiliary battery terminal 200 Ω or higher
      A50-22 (LCH) - GND Cable disconnected from negative (-) auxiliary battery terminal 200 Ω or higher
      A50-21 (LCL) - +B Cable disconnected from negative (-) auxiliary battery terminal 6 kΩ or higher
      A50-22 (LCH) - +B Cable disconnected from negative (-) auxiliary battery terminal 6 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE CAN BUS MAIN LINE OR CONNECTOR 

    Result: 

    OK 

    See step  20

  20. REPLACE HEADLIGHT ECU SUB-ASSEMBLY RH 
    1. Replace the headlight ECU sub-assembly RH with a new or known good one.

      Refer to REMOVAL [10/2015 - 08/2016] , or refer to REMOVAL [08/2016 - 08/2019]

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  21

  21. CLEAR DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Clear DTCs 

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  22

  22. CHECK FOR DTC 
    1. Turn the power switch on (IG).
    2. Check for DTCs.

      Refer to DTC CHECK / CLEAR [10/2015 - 08/2019]

      Body Electrical > AFS > Trouble Codes 

      OK

      DTC U0242 is not output.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    END (HEADLIGHT ECU SUB-ASSEMBLY RH WAS DEFECTIVE) 

    Result: 

    NG 

    REPLACE HEADLIGHT ECU SUB-ASSEMBLY LH. Refer to  REMOVAL [10/2015 - 08/2016]  , or refer to  REMOVAL [08/2016 - 08/2019] 

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