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Home >> Toyota >> 2021 >> Mirai XLE >> Repair and Diagnosis >> Accessories & Equipment >> Exterior Lights >> Lighting System (W/O Headlight Ecu) - Diagnostic Codes & Circuit Tests >> LIGHTING SYSTEM (w/o Headlight ECU) >> LO-beam Headlight does not Illuminate [11/2020 - 12/2023] >> Procedure

LO-beam Headlight does not Illuminate [11/2020 - 12/2023]: Procedure

  1. PERFORM ACTIVE TEST USING GTS 
    1. Perform the Active Test according to the display on the GTS.

      Body Electrical > Main Body > Active Test 

      Tester Display Measurement Item Control Range Diagnostic Note
      Headlight Relay Low beam headlights OFF or ON -

      Body Electrical > Main Body > Active Test 

      Tester Display
      Headlight Relay

      OK

      Low beam headlights illuminate.

      Result

      Result Proceed to
      OK A
      NG (for LH Side) B
      NG (for RH Side) C

    Result: 

    A 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [11/2020 - ] 

    Result: 

    C 

    See step  9

    Result: 

    B 

    See step  2

  2. CHECK HEADLIGHT ASSEMBLY LH (LO TERMINAL VOLTAGE) 
    1. Disconnect the A29 headlight assembly LH connector.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      A29-3 (LO) - Body ground Light control switch in HEAD position 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  4

    Result: 

    OK 

    See step  3

  3. CHECK HARNESS AND CONNECTOR (HEADLIGHT ASSEMBLY LH - BODY GROUND) 
    1. Disconnect the A29 headlight assembly LH connector.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A29-4 (E) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE HEADLIGHT ASSEMBLY LH. Refer to  DISASSEMBLY [11/2020 - 11/2021]  , or refer to  DISASSEMBLY [11/2021 - 12/2023] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  4. INSPECT H-LP LH RELAY 

    Refer to ON-VEHICLE INSPECTION [11/2020 - ]

    Result

    Proceed to
    OK
    NG

    Result: 

    NG 

    REPLACE H-LP LH RELAY 

    Result: 

    OK 

    See step  5

  5. CHECK HARNESS AND CONNECTOR (H-LP LH RELAY - HEADLIGHT ASSEMBLY LH) 
    1. Remove the H-LP LH relay.
    2. Disconnect the A29 headlight assembly LH connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      5 (H-LP LH relay) - A29-3 (LO) Always Below 1 Ω
      5 (H-LP LH relay) or A29-3 (LO) - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  6

  6. CHECK HARNESS AND CONNECTOR (H-LP LH RELAY - BATTERY) 
    1. Remove the H-LP LH relay.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      1 (H-LP LH relay) - Body ground Ignition switch off 11 to 14 V
      3 (H-LP LH relay) - Body ground Ignition switch off 11 to 14 V
      GTY510431Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to H-LP LH Relay)

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (H-LP LH RELAY - DRIVER SIDE JUNCTION BLOCK ASSEMBLY) 
    1. Remove the H-LP LH relay.
    2. Disconnect the 4F driver side junction block assembly connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      2 (H-LP LH relay) - 4F-19 Always Below 1 Ω
      2 (H-LP LH relay) or 4F-19 - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. INSPECT DRIVER SIDE JUNCTION BLOCK ASSEMBLY 
    GTY895500Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    *a Component without harness connected
    (Driver Side Junction Block Assembly)    		 - -
    1. Remove the driver side junction block assembly.

      Refer to REMOVAL [11/2020 - 11/2021] , or refer to REMOVAL [11/2021 - 12/2022] , or refer to REMOVAL [12/2022 - 12/2023]

    2. Remove the main body ECU (multiplex network body ECU) from the driver side junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      4F-19 - A-15 (HRLY) Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU). Refer to  REMOVAL [11/2020 - 11/2021]  , or refer to  REMOVAL [11/2021 - 12/2022]  , or refer to  REMOVAL [12/2022 - 12/2023] 

    Result: 

    NG 

    REPLACE DRIVER SIDE JUNCTION BLOCK ASSEMBLY. Refer to  REMOVAL [11/2020 - 11/2021]  , or refer to  REMOVAL [11/2021 - 12/2022]  , or refer to  REMOVAL [12/2022 - 12/2023] 

  9. INSPECT HEADLIGHT ASSEMBLY RH (LO TERMINAL VOLTAGE) 
    1. Disconnect the A28 headlight assembly RH connector.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      A28-3 (LO) - Body ground Light control switch in HEAD position 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  11

    Result: 

    OK 

    See step  10

  10. CHECK HARNESS AND CONNECTOR (HEADLIGHT ASSEMBLY RH - BODY GROUND) 
    1. Disconnect the A28 headlight assembly RH connector.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A28-4 (E) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE HEADLIGHT ASSEMBLY RH. Refer to  DISASSEMBLY [11/2020 - 11/2021]  , or refer to  DISASSEMBLY [11/2021 - 12/2023] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  11. INSPECT H-LP RH RELAY 

    Refer to ON-VEHICLE INSPECTION [11/2020 - ]

    Result

    Proceed to
    OK
    NG

    Result: 

    NG 

    REPLACE H-LP RH RELAY 

    Result: 

    OK 

    See step  12

  12. CHECK HARNESS AND CONNECTOR (H-LP RH RELAY - HEADLIGHT ASSEMBLY RH) 
    1. Remove the H-LP RH relay.
    2. Disconnect the A28 headlight assembly RH connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      3 (H-LP RH relay) - A28-3 (LO) Always Below 1 Ω
      3 (H-LP RH relay) or A28-3 (LO) - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  13

  13. CHECK HARNESS AND CONNECTOR (H-LP RH RELAY - BATTERY) 
    1. Remove the H-LP RH relay.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      1 (H-LP RH relay) - Body ground Ignition switch off 11 to 14 V
      5 (H-LP RH relay) - Body ground Ignition switch off 11 to 14 V
      GTY510431Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to H-LP RH Relay)

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  14

  14. CHECK HARNESS AND CONNECTOR (H-LP RH RELAY - MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)) 
    1. Remove the H-LP RH relay.
    2. Disconnect the D11 main body ECU (multiplex network body ECU) connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      2 (H-LP RH relay) - D11-12 (-S) Always Below 1 Ω
      2 (H-LP RH relay) or D11-12 (-S) - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU). Refer to  REMOVAL [11/2020 - 11/2021]  , or refer to  REMOVAL [11/2021 - 12/2022]  , or refer to  REMOVAL [12/2022 - 12/2023] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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