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HOMESERVICE MANUALSTOYOTA2012PRIUS THREEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 129 (PRE-COLLISION SYSTEM (PLUG-IN) (DIAGNOSTIC CODES & CIRCUIT TESTS))PRE-COLLISION SYSTEMDTC C1A4B: STOP LIGHT RELAY CIRCUITPROCEDURE
2012 Toyota Prius Three

DTC C1A4B: Stop Light Relay Circuit: Procedure

2012 Toyota Prius ThreeSECTION Procedure
WARNING: This page is about a different variant/trim than selected.
  1. CHECK DTC OUTPUT (ELECTRONICALLY CONTROLLED BRAKE SYSTEM) 
    1. Check DTC for electronically controlled brake system. Refer to DTC CHECK / CLEAR .

      OK

      Electronically controlled brake system DTC is not output.

    NG → See step   5 

    OK: Go to next step 

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

    NEXT: Go to next step 

  3. CHECK DTC OUTPUT (PRE-COLLISION SYSTEM) 
    1. Using the Techstream, enter the following menus: Body Electrical / Pre-Collision 2 / Trouble Codes.
    2. Clear the DTCs. Refer to DTC CHECK / CLEAR .
    3. Check for DTCs.

      OK

      DTC C1A4B is not output.

    NG → See step   4 

    OK → END (BRAKE BOOSTER WITH MASTER CYLINDER WAS DEFECTIVE) 

  4. REPLACE DRIVING SUPPORT ECU. Refer to  REMOVAL 
  5. GO TO ELECTRONICALLY CONTROLLED BRAKE SYSTEM. Refer to  DIAGNOSTIC TROUBLE CODE CHART 
RENDER: 1.0x

NO RELATED

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.