LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 2013 >> Prius Four >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Cruise Control Systems >> Dynamic Radar Cruise Control System (Diagnostic Codes & Circuit Tests) (Except Plug-In) >> Dynamic Radar Cruise Control System >> DTC C1A05: Stop Light Switch Circuit; DTC C1A4B: Stop Light Relay Circuit >> Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC C1A05: Stop Light Switch Circuit; DTC C1A4B: Stop Light Relay Circuit: Procedure

  1. CHECK FOR DTCs 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch on (IG).
    3. Turn the Techstream on.
    4. Enter the following menus: Powertrain / Radar Cruise / Trouble Codes.
    5. Check for DTCs.

      Result

      Result Proceed to
      DTC C1A05 is output A
      DTC C1A4B is output B
    6. Turn the power switch off.

    B → See step   15 

    A: Go to next step 

  2. CHECK STOP LIGHT OPERATION 
    1. Check that the stop lights come on when the brake pedal is depressed, and go off when the brake pedal is released.

      OK

      Condition Illumination Condition
      Brake pedal depressed ON
      Brake pedal released OFF

    NG → See step   31 

    OK: Go to next step 

  3. READ VALUE USING TECHSTREAM (STOP LIGHT SWITCH ASSEMBLY) 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch on (IG).
    3. Turn the Techstream on.
    4. Enter the following menus: Powertrain / Radar Cruise / Data List.
    5. Check the Data List for proper functioning of the stop light switch.
      RADAR CRUISE

      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      Stop Light SW 1 (M CPU) Stop light switch (Main-CPU) signal / ON or OFF ON: Brake pedal depressed
      OFF: Brake pedal released      		 -
      Stop Light SW 1 (S CPU) Stop light switch (Sub-CPU) signal / ON or OFF ON: Brake pedal depressed
      OFF: Brake pedal released      		 -
      Stop Light SW 2 (M CPU) Stop light switch (Main-CPU) signal / ON or OFF ON: Brake pedal depressed
      OFF: Brake pedal released      		 -

      OK

      Display changes according to brake pedal operation described in above table.

    NG → See step   11 

    OK: Go to next step 

  4. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - SKID CONTROL ECU) 
    1. Disconnect the stop light switch assembly connector.
    2. Disconnect the brake booster with master cylinder (skid control ECU) connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Condition Specified Condition
      A67-2 (L) - A58-33 (STP) Always Below 1 Ω

      Standard Resistance (Check for Short)

      Tester Connection Condition Specified Condition
      A67-2 (L) or A58-33 (STP) - Body ground Always 10 kΩ or higher
    4. Reconnect the stop light switch assembly connector.
    5. Reconnect the brake booster with master cylinder (skid control ECU) connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - SKID CONTROL ECU) 

    OK: Go to next step 

  5. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL RELAY - SKID CONTROL ECU) 
    1. Disconnect the stop light control relay assembly connector.
    2. Disconnect the brake booster with master cylinder (skid control ECU) connectors.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Condition Specified Condition
      A28-1 (OUT) - A58-6 (STP2) Always Below 1 Ω
      A28-5 (STP) - A58-33 (STP) Always Below 1 Ω
      A28-9 (ACC) - A58-3 (STP0) Always Below 1 Ω

      Standard Resistance (Check for Short)

      Tester Connection Condition Specified Condition
      A28-1 (OUT) or A58-6 (STP2) - Body ground Always 10 kΩ or higher
      A28-5 (STP) or A58-33 (STP) - Body ground Always 10 kΩ or higher
      A28-9 (ACC) or A58-3 (STP0) - Body ground Always 10 kΩ or higher
    4. Reconnect the stop light control relay connector.
    5. Reconnect the brake booster with master cylinder (skid control ECU) connectors.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT CONTROL RELAY - SKID CONTROL ECU) 

    OK: Go to next step 

  6. INSPECT STOP LIGHT CONTROL RELAY 
    1. Inspect the stop light control relay. Refer to INSPECTION .

    NG → See step   28 

    OK: Go to next step 

  7. REPLACE BRAKE BOOSTER WITH MASTER CYLINDER (SKID CONTROL ECU) 
    1. Replace the brake booster with master cylinder (skid control ECU). Refer to REMOVAL .

    NEXT: Go to next step 

  8. CHECK FOR DTCs (DTC C1A05) 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch on (IG).
    3. Clear the DTCs. Refer to DTC CHECK / CLEAR .
    4. Perform the following to make sure that the DTC detection conditions are met.

      HINT: 

      If the detection conditions are not met, the malfunction cannot be detected.

      1. Drive the vehicle at a speed of between approximately 50 km/h (30 mph) and 170 km/h (105 mph).
      2. Turn the cruise control system on using the cruise control switch (ON-OFF button).
      3. Push the cruise control switch to -/SET to begin control of vehicle speed using the cruise control system.
    5. Enter the following menus: Powertrain / Radar Cruise / Trouble Codes.
    6. Check for DTCs.

      Result

      Result Proceed to
      DTC is not output A
      DTC C1A05 is output B

    B → See step   9 

    A → END 

  9. REPLACE POWER MANAGEMENT CONTROL ECU 
    1. Replace the power management control ECU. Refer to REMOVAL .

    NEXT: Go to next step 

  10. CHECK FOR DTCs (DTC C1A05) 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch on (IG).
    3. Clear the DTCs. Refer to DTC CHECK / CLEAR .
    4. Perform the following to make sure that the DTC detection conditions are met.

      HINT: 

      If the detection conditions are not met, the malfunction cannot be detected.

      1. Drive the vehicle at a speed of between approximately 50 km/h (30 mph) and 170 km/h (105 mph).
      2. Turn the cruise control system on using the cruise control switch (ON-OFF button).
      3. Push the cruise control switch to -/SET to begin control of vehicle speed using the cruise control system.
    5. Enter the following menus: Powertrain / Radar Cruise / Trouble Codes.
    6. Check for DTCs.

      Result

      Result Proceed to
      DTC is not output A
      DTC C1A05 is output B

    B → See step   29 

    A → END 

  11. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - POWER SOURCE) 
    1. Disconnect the stop light switch assembly connector.
      Fig 1: Identifying Stop Light Switch Assembly Connector Terminals
      GTY337419Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the voltage and resistance according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A67-1 (B) - A67-3 (GND) Power switch off 11 to 14 V
      A67-5 (B) - A67-3 (GND) Power switch on (IG) 11 to 14 V

      Standard Resistance

      Tester Connection Condition Specified Condition
      A67-3 (GND) - Body ground Always Below 1 Ω
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Stop Light Switch Assembly)
    3. Reconnect the stop light switch assembly connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH - IG2 RELAY) 

    OK: Go to next step 

  12. INSPECT STOP LIGHT SWITCH ASSEMBLY 
    1. Remove the stop light switch assembly. Refer to REMOVAL .
      Fig 2: Identifying Stop Light Switch Assembly Connector Terminals
      GTY341439Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      TEXT IN ILLUSTRATION

      *a Component with harness connected
      (Stop Light Switch Assembly)
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      A67-2 (L) - A67-3 (GND) Power switch off, Brake pedal not depressed Below 1 V
      A67-4 (L) - A67-3 (GND) 11 to 14 V
      A67-2 (L) - A67-3 (GND) Power switch off, Brake pedal depressed 11 to 14 V
      A67-4 (L) - A67-3 (GND) Below 1 V

    NG → See step   27 

    OK: Go to next step 

  13. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - DRIVING SUPPORT ECU) 
    1. Disconnect the driving support ECU connector.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Condition Specified Condition
      A67-2 (L) - L60-27 (STP-) Always Below 1 Ω
      A67-4 (L) - L60-28 (ST1-) Always Below 1 Ω

      Standard Resistance (Check for Short)

      Tester Connection Condition Specified Condition
      A67-2 (L) or L60-27 (STP-) - Body ground Always 10 kΩ or higher
      A67-4 (L) or L60-28 (ST1-) - Body ground Always 10 kΩ or higher
    3. Reconnect the stop light switch assembly connector.
    4. Reconnect the driving support ECU connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - DRIVING SUPPORT ECU) 

    OK: Go to next step 

  14. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - BODY GROUND) 
    1. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Short)

      Tester Connection Condition Specified Condition
      A67-2 (L) - Body ground Always 10 kΩ or higher
      A67-4 (L) - Body ground Always 10 kΩ or higher
    2. Reconnect the stop light switch assembly connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - BODY GROUND) 

    OK → See step   30 

  15. CHECK FOR DTCs (ABS/VSC/TRAC) 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch on (IG).
    3. Turn the Techstream on.
    4. Enter the following menus: Chassis / ABS/VSC/TRAC / Trouble Codes.
    5. Check for DTCs.

      Result

      Result Proceed to
      DTC is not output A
      DTC is output B
    6. Turn the power switch off.

    B → See step   34 

    A: Go to next step 

  16. CHECK STOP LIGHT OPERATION 
    1. Check that the stop lights come on when the brake pedal is depressed, and go off when the brake pedal is released.

      OK

      Condition Illumination Condition
      Brake pedal depressed ON
      Brake pedal released OFF

    NG → See step   35 

    OK: Go to next step 

  17. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL RELAY POWER SOURCE) 
    1. Disconnect the stop light control relay connector.
      Fig 3: Checking Harness And Connector (Stop Light Control Relay Power Source) With A28 Connector End View
      GTY361838Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A28-6 (+B) - Body ground Always 11 to 14 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Stop Light Control Relay)
    3. Reconnect the stop light control relay connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT CONTROL RELAY - STOP FUSE) 

    OK: Go to next step 

  18. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL RELAY - BODY GROUND) 
    1. Disconnect the stop light control relay connector.
      Fig 4: Checking Harness And Connector (Stop Light Control Relay - Body Ground) With A28 Connector End View
      GTY381363Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Condition Specified Condition
      A28-8 (GND) - Body ground Always Below 1 Ω
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Stop Light Control Relay)
    3. Reconnect the stop light control relay connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT CONTROL RELAY - BODY GROUND) 

    OK: Go to next step 

  19. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL RELAY - STOP LIGHT SWITCH ASSEMBLY) 
    1. Turn the power switch off.
      Fig 5: Checking Harness And Connector (Stop Light Control Relay - Stop Light Switch Assembly) With A28 Connector End View
      GTY381418Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Disconnect the stop light control relay connector.
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      A28-5 (STP) - Body ground Stop light switch ON (Brake pedal depressed) 11 to 14 V
      A28-5 (STP) - Body ground Stop light switch OFF (Brake pedal released) Below 2 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Stop Light Control Relay)
    4. Reconnect the stop light control relay connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT CONTROL RELAY - STOP LIGHT SWITCH ASSEMBLY) 

    OK: Go to next step 

  20. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - SKID CONTROL ECU) 
    1. Turn the power switch off.
    2. Make sure that there is no looseness at the locking part and the connecting part of the connector.
    3. Disconnect the brake booster with master cylinder (skid control ECU) connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      A58-33 (STP) - Body ground Stop light switch ON (Brake pedal depressed) 11 to 14 V
      A58-33 (STP) - Body ground Stop light switch OFF (Brake pedal released) Below 1.5 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Skid Control ECU)
    5. Reconnect the brake booster with master cylinder (skid control ECU) connector.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - SKID CONTROL ECU) 

    OK: Go to next step 

  21. PERFORM ACTIVE TEST USING TECHSTREAM (STOP LIGHT RELAY) 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch on (IG).
    3. Turn the Techstream on.
    4. Enter the following menus: Chassis / ABS/VSC/TRAC / Active Test.
    5. Select the Active Test on the Techstream.
      ABS/VSC/TRAC

      Tester Display Test Part Control Range Diagnostic Note
      Stop Light Relay Stop light control relay Relay ON/OFF Stop lights come on
    6. Select the Data List on the Techstream.
      ABS/VSC/TRAC

      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      Stop Light Relay Output Stop light control relay output / ON or OFF ON: Relay output on
      OFF: Relay output off      		 -
    7. Check stop light control relay operation and stop light operation on the Data List while performing the Active Test.

      Result

      Result Proceed to
      Data List content and stop light operation are abnormal or Data List content is normal but stop lights do not turn on or off. A
      Data List content and stop light operation are normal. B
    8. Turn the power switch off.

    B → See step   23 

    A: Go to next step 

  22. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL RELAY - SKID CONTROL ECU) 
    1. Disconnect the stop light control relay connector.
    2. Disconnect the brake booster with master cylinder (skid control ECU) connectors.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Switch Condition Specified Condition
      A28-9 (ACC) - A58-3 (STP0) Always Below 1 Ω

      Standard Resistance (Check for Short)

      Tester Connection Switch Condition Specified Condition
      A28-9 (ACC) or A58-3 (STP0) - Body ground Always 10 kΩ or higher
    4. Reconnect the stop light control relay connector.
    5. Reconnect the brake booster with master cylinder (skid control ECU) connectors.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT CONTROL RELAY - SKID CONTROL ECU) 

    OK: Go to next step 

  23. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL RELAY - SKID CONTROL ECU) 
    1. Disconnect the stop light control relay connector.
    2. Disconnect the brake booster with master cylinder (skid control ECU) connectors.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)

      Tester Connection Switch Condition Specified Condition
      A28-1 (OUT) - A58-6 (STP2) Always Below 1 Ω
    4. Reconnect the stop light control relay connector.
    5. Reconnect the brake booster with master cylinder (skid control ECU) connectors.

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT CONTROL RELAY - SKID CONTROL ECU) 

    OK: Go to next step 

  24. INSPECT STOP LIGHT CONTROL RELAY 
    1. Inspect the stop light control relay. Refer to INSPECTION .

    NG → See step   32 

    OK: Go to next step 

  25. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL RELAY - SKID CONTROL ECU) 
    1. Turn the power switch off.
    2. Disconnect the brake booster with master cylinder (skid control ECU) connectors.
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      A58-6 (STP2) - Body ground Stop light switch ON (Brake pedal depressed) 11 to 14 V
      A58-6 (STP2) - Body ground Stop light switch OFF (Brake pedal released) Below 1.5 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Skid Control ECU)
    4. Reconnect the brake booster with master cylinder (skid control ECU) connectors.

    NG → See step   32 

    OK: Go to next step 

  26. CHECK FOR DTCs (DTC C1A4B) 
    1. Connect the Techstream to the DLC3.
    2. Turn the power switch on (IG).
    3. Clear the DTCs. Refer to DTC CHECK / CLEAR .
    4. Perform the following to make sure that the DTC detection conditions are met.

      HINT: 

      If the detection conditions are not met, the malfunction cannot be detected.

      1. Drive the vehicle at a speed of 50 km/h (30 mph) and 170 km/h (105 mph).
      2. Turn the cruise control switch (ON-OFF button) on.
      3. Push the -/SET switch to activate the cruise control.
    5. Enter the following menus: Powertrain / Radar Cruise / Trouble Codes.
    6. Read the DTC.

      Result

      Result Proceed to
      DTC is not output A
      DTC C104B is output B

    B → See step   33 

    A → END 

  27. REPLACE STOP LIGHT SWITCH ASSEMBLY. Refer to  REMOVAL 
  28. REPLACE STOP LIGHT CONTROL RELAY. Refer to  REMOVAL 
  29. REPLACE DRIVING SUPPORT ECU. Refer to  REMOVAL 
  30. REPLACE DRIVING SUPPORT ECU. Refer to  REMOVAL 
  31. GO TO LIGHTING SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING 
  32. REPLACE STOP LIGHT CONTROL RELAY. Refer to  COMPONENTS 
  33. REPLACE DRIVING SUPPORT ECU ASSEMBLY. Refer to  COMPONENTS 
  34. GO TO ELECTRONICALLY CONTROLLED BRAKE SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING 
  35. GO TO LIGHTING SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING 
scientia non olet · About LEMON Manuals