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HOMESERVICE MANUALSTOYOTA2012PRIUS THREEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 41 (ENGINE CONTROL SYSTEM (PLUG-IN) (DIAGNOSTIC CODES (P0505-U0293) & CIRCUIT TESTS))SFI SYSTEMCIRCUIT TESTSECM POWER SOURCE CIRCUITPROCEDURE
2012 Toyota Prius Three

ECM Power Source Circuit: Procedure

2012 Toyota Prius ThreeSECTION Procedure
WARNING: This page is about a different variant/trim than selected.
  1. CHECK HARNESS AND CONNECTOR (ECM - BODY GROUND) 
    1. Disconnect the ECM connector.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      D28-104 (E1) - Body ground Always Below 1 Ω

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

    OK: Go to next step 

  2. INSPECT ECM (IGSW VOLTAGE) 
    1. Disconnect the ECM connector.
      Fig 1: Inspecting ECM (IGSW Voltage)
      GTY343347Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. Turn the power switch on (IG).
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A57-28 (IGSW) - Body ground Power switch on (IG) 11 to 14 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to ECM)

    NG → See step   7 

    OK: Go to next step 

  3. INSPECT NO. 2 INTEGRATION RELAY (EFI MAIN RELAY) 
    1. Inspect the No. 2 integration relay (EFI MAIN relay). Refer to INSPECTION .

    NG → See step   13 

    OK: Go to next step 

  4. CHECK HARNESS AND CONNECTOR (NO. 2 INTEGRATION RELAY (EFI MAIN RELAY) - ECM) 
    1. Remove the No. 2 integration relay (EFI MAIN relay) from the engine room relay block and junction block assembly.
    2. Disconnect the ECM connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      1B-4 - A57-1 (+B2) Always Below 1 Ω
      1B-4 - A57-2 (+B) Always Below 1 Ω
      1B-2 - A57-6 (MREL) Always Below 1 Ω

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

    OK: Go to next step 

  5. CHECK HARNESS AND CONNECTOR (NO. 2 INTEGRATION RELAY (EFI MAIN RELAY) - BODY GROUND) 
    1. Remove the No. 2 integration relay (EFI MAIN relay) from the engine room relay block and junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      1B-3 - Body ground Always Below 1 Ω

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

    OK → See step   6 

  6. PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE. Refer to  PROBLEM SYMPTOMS TABLE 
  7. INSPECT NO. 2 INTEGRATION RELAY (IG2 RELAY) 
    1. Inspect the No. 2 integration relay (IG2 relay). Refer to INSPECTION .

    NG → See step   14 

    OK: Go to next step 

  8. CHECK HARNESS AND CONNECTOR (NO. 2 INTEGRATION RELAY (IG2 RELAY) - ECM) 
    1. Disconnect the ECM connector.
    2. Remove the No. 2 integration relay (IG2 relay) from the engine room relay block and junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      1A-4 - A57-28 (IGSW) Always Below 1 Ω

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

    OK: Go to next step 

  9. CHECK HARNESS AND CONNECTOR (NO. 2 INTEGRATION RELAY (IG2 RELAY) - AUXILIARY BATTERY) 
    1. Remove the No. 2 integration relay (IG2 relay) from the engine room relay block and junction block assembly.
    2. Disconnect the negative (-) auxiliary battery terminal.
    3. Disconnect the positive (+) auxiliary battery terminal.
    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      1C-1 - Positive (+) auxiliary battery terminal Always Below 1 Ω

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

    OK: Go to next step 

  10. CHECK HARNESS AND CONNECTOR (NO. 2 INTEGRATION RELAY (IG2 RELAY) - BODY GROUND) 
    1. Remove the No. 2 integration relay (IG2 relay) from the engine room relay block and junction block assembly.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      1A-3 - Body ground Always Below 1 Ω

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

    OK: Go to next step 

  11. CHECK HARNESS AND CONNECTOR (POWER MANAGEMENT CONTROL ECU - NO. 2 INTEGRATION RELAY) 
    1. Remove the No. 2 integration relay (IG2 relay) from the engine room relay block and junction block assembly.
    2. Disconnect the power management control ECU connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A86-2 (IG2D) - 1A-2 Always Below 1 Ω

    NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

    OK → See step   12 

  12. CHECK SMART KEY SYSTEM (FOR ENTRY FUNCTION). Refer to  HOW TO PROCEED WITH TROUBLESHOOTING 
  13. REPLACE NO. 2 INTEGRATION RELAY (EFI MAIN RELAY). Refer to  REMOVAL 
  14. REPLACE NO. 2 INTEGRATION RELAY (IG2 RELAY). Refer to  REMOVAL 
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.