LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 2014 >> Corolla LE >> Repair and Diagnosis (Single Page) >> Restraints >> Restraints Control Systems >> Pre-Collision System - Diagnostic Codes & Circuit Tests (Model Code: ZRE172) >> Pre-Collision System >> DTC C1A4B: Stop Light Relay Circuit [08/2016 - ] >> Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC C1A4B: Stop Light Relay Circuit [08/2016 - ]: Procedure

  1. INSPECT TERMINAL VOLTAGE (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) CONNECTOR) 
    1. Turn the ignition switch off.
    2. Disconnect the A43 skid control ECU (brake actuator assembly) connector.
      GTY695337Courtesy 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
      A43-26 (STPO) - Body ground Ignition switch ON 10 to 16 V
      A43-35 (STP) - Body ground Brake pedal depressed 8 to 16 V
      Brake pedal released Below 1.5 V
      A43-5 (STP2) - Body ground Brake pedal depressed 8 to 16 V
      Brake pedal released Below 1.5 V
    4. Connect the A43 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 STPO is not as specified. B
      Only the voltage at terminal STP is not as specified. C
      Only the voltage at terminal STP2 is not as specified. D
      The voltage at both terminal STPO and terminal STP are not as specified. E

    Result:  2

    B 

    See step  5

    Result:  3

    C 

    See step  12

    Result:  4

    D 

    See step  13

    Result:  5

    E 

    See step  14

    Result:  1

    A 

    See step  2

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

      Refer to DATA LIST / ACTIVE TEST [08/2016 - ]

      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:  2

    NG 

    See step  4

    Result:  1

    OK 

    See step  3

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

      Refer to DTC CHECK / CLEAR [08/2016 - ]

      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 [08/2016 - ]

      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 [08/2016 - ]

      Body Electrical > Pre-Collision 2 > Trouble Codes 

      OK

      DTC C1A4B is not output

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    USE SIMULATION METHOD TO CHECK:  HOW TO PROCEED WITH TROUBLESHOOTING [08/2016 - 08/2017]  Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [08/2017 - ] 

    Result:  2

    NG 

    REPLACE SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY):  COMPONENTS [08/2015 - 08/2017]  Refer to  COMPONENTS [08/2017 - ] 

  4. INSPECT STOP LIGHT RELAY 
    1. Inspect the stop light relay.

      Refer to ON-VEHICLE INSPECTION [08/2016 - ]

      OK

      The stop light relay is normal.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPLACE SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY):  COMPONENTS [08/2015 - 08/2017]  Refer to  COMPONENTS [08/2017 - ] 

    Result:  2

    NG 

    REPLACE STOP LIGHT RELAY 

  5. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - STOP LIGHT RELAY) 
    1. Turn the ignition switch off.
    2. Remove the stop light relay from the engine room relay block and junction block assembly.
      GTY711817Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Engine Room Relay Block and Junction Block Assembly (Relay Holder)
    3. Disconnect the A43 skid control ECU (brake actuator assembly) connector.
      GTY732841Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Skid control ECU (brake actuator assembly))
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A43-26 (STPO) - Relay holder terminal 1 Always Below 1 Ω
    5. Connect the A43 skid control ECU (brake actuator assembly) connector.
    6. Install the stop light relay to the engine room relay block and junction block assembly.

      Result

      Proceed to
      OK
      NG

    Result:  2

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result:  1

    OK 

    See step  6

  6. INSPECT STOP LIGHT RELAY (STOP LIGHT RELAY POWER SOURCE) 
    1. Turn the ignition switch off.
    2. Remove the stop light relay from the engine room relay block and junction block assembly.
      GTY711817Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Engine Room Relay Block and Junction Block Assembly (Relay Holder)
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      Relay holder terminal 2 - Body ground Ignition switch ON 11 to 14 V
      Relay holder terminal 5 - Body ground Always 11 to 14 V
    4. Install the stop light relay to the engine room relay block and junction block assembly.

      Result

      Proceed to
      OK
      NG

    Result:  2

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result:  1

    OK 

    See step  7

  7. INSPECT STOP LIGHT RELAY 
    1. Inspect the stop light relay.

      Refer to ON-VEHICLE INSPECTION [08/2016 - ]

      OK

      The stop light relay is normal.

      Result

      Proceed to
      OK
      NG

    Result:  2

    NG 

    REPLACE STOP LIGHT RELAY 

    Result:  1

    OK 

    See step  8

  8. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY LH) 
    1. Turn the ignition switch off.
    2. Disconnect the A43 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the L22 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
      A43-35 (STP) or L22-3 (STP) - Body ground Brake pedal depressed 8 to 16 V
    5. Connect the L22 rear combination light assembly LH connector.
    6. Connect the A43 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPLACE REAR COMBINATION LIGHT ASSEMBLY LH:  COMPONENTS [08/2013 - ] 

    Result:  2

    NG 

    See step  9

  9. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - CENTER STOP LIGHT ASSEMBLY) 
    1. Turn the ignition switch off.
    2. Disconnect the A43 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the g1 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
      A43-35 (STP) or g1-1 (B) - Body ground Brake pedal depressed 8 to 16 V
    5. Connect the g1 center stop light assembly connector.
    6. Connect the A43 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPLACE CENTER STOP LIGHT ASSEMBLY:  COMPONENTS [08/2013 - ] 

    Result:  2

    NG 

    See step  10

  10. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY RH) 
    1. Turn the ignition switch off.
    2. Disconnect the A43 skid control ECU (brake actuator assembly) connector.
    3. Disconnect the L21 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
      A43-35 (STP) or L21-3 (STP) - Body ground Brake pedal depressed 8 to 16 V
    5. Connect the L21 rear combination light assembly RH connector.
    6. Connect the A43 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPLACE REAR COMBINATION LIGHT ASSEMBLY RH:  COMPONENTS [08/2013 - ] 

    Result:  2

    NG 

    See step  11

  11. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - STOP LIGHT RELAY) 
    1. Turn the ignition switch off.
    2. Disconnect the A43 skid control ECU (brake actuator assembly) connector.
    3. Remove the stop light relay from the engine room relay block and junction block assembly.
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      Relay holder terminal 3 or A43-35 (STP) - Body ground Always 10 kΩ or higher
    5. Install the stop light relay to the engine room relay block and junction block assembly.
    6. Connect the A43 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPLACE STOP LIGHT RELAY 

    Result:  2

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  12. INSPECT STOP LIGHT RELAY 
    1. Inspect the stop light relay.

      Refer to ON-VEHICLE INSPECTION [08/2016 - ]

      OK

      The stop light relay is normal.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result:  2

    NG 

    REPLACE STOP LIGHT RELAY 

  13. INSPECT STOP LIGHT RELAY 
    1. Inspect the stop light relay.

      Refer to ON-VEHICLE INSPECTION [08/2016 - ]

      OK

      The stop light relay is normal.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result:  2

    NG 

    REPLACE STOP LIGHT RELAY 

  14. CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - STOP LIGHT RELAY) 
    1. Turn the ignition switch off.
    2. Disconnect the A43 skid control ECU (brake actuator assembly) connector.
    3. Remove the stop light relay from the engine room relay block and junction block assembly.
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A43-26 (STPO) or relay holder terminal 1 - Body ground Always 10 kΩ or higher
    5. Install the stop light relay to the engine room relay block and junction block assembly.
    6. Connect the A43 skid control ECU (brake actuator assembly) connector.

      Result

      Proceed to
      OK
      NG

    Result:  1

    OK 

    REPLACE STOP LIGHT RELAY 

    Result:  2

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

scientia non olet · About LEMON Manuals