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Home >> Lexus >> 2023 >> RC F Base >> Repair and Diagnosis (Single Page) >> Restraints >> Restraints Control Systems >> Pre-Collision System - Diagnostic Codes (1 Of 2) >> Pre-Collision System >> DTC C1A4B: Stop Light Relay Circuit [11/2017 - 03/2019] >> Procedure

DTC C1A4B: Stop Light Relay Circuit [11/2017 - 03/2019]: Procedure

  1. INSPECT TERMINAL VOLTAGE (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) CONNECTOR) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
      GTY829179Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Skid control ECU (brake actuator assembly))
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-35 (STP) - Body ground Brake pedal depressed 11 to 14 V
      Brake pedal released Below 1.5 V
      A86-26 (STPO) - Body ground Always 11 to 14 V
      A86-5 (STP2) - Body ground Brake pedal depressed 11 to 14 V
      Brake pedal released Below 1.5 V
    4. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Result Proceed to
      The voltage is as specified for every terminal. A
      Only the voltage at terminal STP is not as specified. B
      Only the voltage at terminal STPO is not as specified. C
      Only the voltage at terminal STP2 is not as specified. D
      The voltage at both terminal STPO and terminal STP2 are not as specified. E

    Result: 

    B 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    C 

    See step  5

    Result: 

    D 

    See step  6

    Result: 

    E 

    See step  19

    Result: 

    A 

    See step  2

  2. PERFORM ACTIVE TEST USING TECHSTREAM (STOP LIGHT RELAY) 
    1. Turn the engine switch off.
    2. According to the display on the Techstream, perform the Active Test Stop Light Relay.

      Refer to DATA LIST / ACTIVE TEST [11/2017 - 03/2019]

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display Measurement Item Control Range Diagnostic Note
      Stop Light Relay Stop Light Relay ON / OFF Stop lights come on
      Vehicle condition: Vehicle stopped

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display
      Stop Light Relay

      OK

      The stop lights turn on and off correctly in response to the operation of the Active Test.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  4

    Result: 

    OK 

    See step  3

  3. 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. According to the display on the Techstream, perform the Active Test Stop Light Relay.

      Refer to DATA LIST / ACTIVE TEST [11/2017 - 03/2019]

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display Measurement Item Control Range Diagnostic Note
      Stop Light Relay Stop Light Relay ON / OFF Stop lights come on
      Vehicle condition: Vehicle stopped

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display
      Stop Light Relay
    3. Check for DTCs.

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

      Body Electrical > Pre-Collision 2 > Trouble Codes 

      OK

      DTC C1A4B is not output

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [11/2017 - 03/2019] 

    Result: 

    NG 

    REPLACE SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY). Refer to  COMPONENTS [11/2017 - 01/2023] 

  4. INSPECT STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU) 
    1. Turn the engine switch off.
    2. Inspect the stop light relay (semiconductor power integration ECU).

      Refer to ON-VEHICLE INSPECTION [09/2014 - ]

      OK

      The stop light relay (semiconductor power integration ECU) is normal.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY). Refer to  COMPONENTS [11/2017 - 01/2023] 

    Result: 

    NG 

    REPLACE STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU). Refer to  COMPONENTS [09/2014 - ] 

  5. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU)) 
    1. Turn the engine switch off.
    2. Remove the stop light relay (semiconductor power integration ECU).
    3. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A86-26 (STPO) - 2D-3 (ACC) Always Below 1 Ω
    5. Connect the A86 skid control ECU (brake actuator assembly) connector.
    6. Install the stop light relay (semiconductor power integration ECU).

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU). Refer to  COMPONENTS [09/2014 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  6. INSPECT TERMINAL VOLTAGE (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) CONNECTOR) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
      GTY783795Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Skid control ECU (brake actuator assembly))
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal released Below 1.5 V
    4. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  13

    Result: 

    OK 

    See step  7

  7. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY LH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U41 rear combination light assembly LH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal depressed 11 to 14 V
    5. Connect the U41 rear combination light assembly LH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR COMBINATION LIGHT ASSEMBLY LH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    See step  8

  8. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY RH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U5 rear combination light assembly RH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal depressed 11 to 14 V
    5. Connect the U5 rear combination light assembly RH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR COMBINATION LIGHT ASSEMBLY RH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    See step  9

  9. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - CENTER STOP LIGHT ASSEMBLY) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U8 center stop light assembly connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal depressed 11 to 14 V
    5. Connect the U8 center stop light assembly connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE CENTER STOP LIGHT ASSEMBLY. Refer to  COMPONENTS [09/2014 - ] 

    Result: 

    NG 

    See step  10

  10. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR LIGHT ASSEMBLY LH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U42 rear light assembly LH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal depressed 11 to 14 V
    5. Connect the U42 rear light assembly LH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR LIGHT ASSEMBLY LH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    See step  11

  11. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR LIGHT ASSEMBLY RH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U6 rear light assembly RH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal depressed 11 to 14 V
    5. Connect the U6 rear light assembly RH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR LIGHT ASSEMBLY RH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    See step  12

  12. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU)) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Remove the stop light relay (semiconductor power integration ECU).
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      2D-10 (STP) - A86-35 (STP) Always Below 1 Ω
      2F-9 (OUT) - A86-5 (STP2) Always Below 1 Ω
      2F-9 (OUT) or A86-5 (STP2) - Body ground Always 10 kΩ or higher
    5. Install the stop light relay (semiconductor power integration ECU).
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU). Refer to  COMPONENTS [09/2014 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  13. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU)) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Remove the stop light relay (semiconductor power integration ECU).
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) or 2F-9 (OUT) - Body ground Brake pedal released Below 1.5 V
    5. Install the stop light relay (semiconductor power integration ECU).
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU). Refer to  COMPONENTS [09/2014 - ] 

    Result: 

    NG 

    See step  14

  14. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY LH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U41 rear combination light assembly LH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal released Below 1.5 V
    5. Connect the U41 rear combination light assembly LH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR COMBINATION LIGHT ASSEMBLY LH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    See step  15

  15. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY RH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U5 rear combination light assembly RH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal released Below 1.5 V
    5. Connect the U5 rear combination light assembly RH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR COMBINATION LIGHT ASSEMBLY RH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    See step  16

  16. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - CENTER STOP LIGHT ASSEMBLY) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U8 center stop light assembly connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal released Below 1.5 V
    5. Connect the U8 center stop light assembly connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE CENTER STOP LIGHT ASSEMBLY. Refer to  COMPONENTS [09/2014 - ] 

    Result: 

    NG 

    See step  17

  17. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR LIGHT ASSEMBLY LH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U42 rear light assembly LH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal released Below 1.5 V
    5. Connect the U42 rear light assembly LH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR LIGHT ASSEMBLY LH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    See step  18

  18. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR LIGHT ASSEMBLY RH) 
    1. Turn the engine switch off.
    2. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the U6 rear light assembly RH connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A86-5 (STP2) - Body ground Brake pedal released Below 1.5 V
    5. Connect the U6 rear light assembly RH connector.
    6. Connect the A86 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE REAR LIGHT ASSEMBLY RH. Refer to  COMPONENTS [09/2014 - 03/2019] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  19. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU)) 
    1. Turn the engine switch off.
    2. Remove the stop light relay (semiconductor power integration ECU).
    3. Disconnect the A86 skid control ECU (brake actuator assembly) connector.
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A86-26 (STPO) or 2D-3 (ACC) - Body ground Always 10 kΩ or higher
    5. Connect the A86 skid control ECU (brake actuator assembly) connector.
    6. Install the stop light relay (semiconductor power integration ECU).

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  20

  20. INSPECT STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU) 
    1. Turn the engine switch off.
    2. Inspect the stop light relay (semiconductor power integration ECU).

      Refer to ON-VEHICLE INSPECTION [09/2014 - ]

      OK

      The stop light relay (semiconductor power integration ECU) is normal.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    NG 

    REPLACE STOP LIGHT RELAY (SEMICONDUCTOR POWER INTEGRATION ECU). Refer to  COMPONENTS [09/2014 - ] 

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