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HOMESERVICE MANUALSTOYOTA2025PRIUS XLE AWDREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - CIRCUIT TESTS (2 OF 2) & SYMPTOM TESTSSFI SYSTEMECM POWER SOURCE CIRCUIT [12/2022 - ]PROCEDURE
2025 Toyota Prius XLE AWD

ECM Power Source Circuit [12/2022 - ]: Procedure

2025 Toyota Prius XLE AWDSECTION Procedure
  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
      A92-10 (E1) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  2

  2. CHECK TERMINAL VOLTAGE (IGP TERMINAL VOLTAGE) 
    1. Disconnect the ECM connector.
    2. Turn the ignition switch to ON.
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A92-2 (IGP) - Body ground Ignition switch ON 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  6

    Result: 

    OK 

    See step  3

  3. INSPECT EFI-MAIN NO. 1 RELAY 

    Refer to PROCEDURE - Step 1

    Result

    Proceed to
    OK
    NG

    Result: 

    NG 

    REPLACE EFI-MAIN NO. 1 RELAY 

    Result: 

    OK 

    See step  4

  4. CHECK HARNESS AND CONNECTOR (EFI-MAIN NO. 1 RELAY - ECM) 
    1. Remove the EFI-MAIN NO. 1, VVT, EFI-MAIN NO. 2 and EFI-MAIN NO. 3 relays from the No. 1 engine room relay block and No. 1 junction block assembly.

      HINT: 

      Remove the VVT, EFI-MAIN NO. 2 and EFI-MAIN NO. 3 relays connected between the checked terminals as the coil inside the relay influences the measurement value.

    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
      5 (EFI-MAIN NO. 1 relay) - A92-9 (+B) Always Below 1 Ω
      5 (EFI-MAIN NO. 1 relay) - A92-35 (+B2) Always Below 1 Ω
      2 (EFI-MAIN NO. 1 relay) - A92-15 (MREL) Always Below 1 Ω
      5 (EFI-MAIN NO. 1 relay) or A92-9 (+B) - Body ground and other terminals Always 10 kΩ or higher
      5 (EFI-MAIN NO. 1 relay) or A92-35 (+B2) - Body ground and other terminals Always 10 kΩ or higher
      2 (EFI-MAIN NO. 1 relay) or A92-15 (MREL) - Body ground and other terminals Always 10 kΩ or higher

      HINT: 

      If a short is detected in any of the above circuits, there may be a malfunction in the circuit of a connected ECU.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  5

  5. CHECK TERMINAL VOLTAGE (POWER SOURCE OF EFI-MAIN NO. 1 RELAY) 
    1. Remove the EFI-MAIN NO. 1 relay from the No. 1 engine room relay block and No. 1 junction block assembly.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      3 (EFI-MAIN NO. 1 relay) - Body ground Always 11 to 14 V
      1 (EFI-MAIN NO. 1 relay) - Body ground Always 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE ECM 

    Refer to REMOVAL [12/2022 - 03/2023] , or refer to REMOVAL [03/2023 - ]

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AUXILIARY BATTERY - EFI-MAIN NO. 1 RELAY) 

  6. INSPECT IGP RELAY 

    Refer to PROCEDURE - Step 6

    Result

    Proceed to
    OK
    NG

    Result: 

    NG 

    REPLACE IGP RELAY 

    Result: 

    OK 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (IGP RELAY - ECM) 
    1. Remove the IGP relay from the No. 1 engine room relay block and No. 1 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
      3 (IGP Relay) - A92-2 (IGP) Always Below 1 Ω
      3 (IGP Relay) or A92-2 (IGP) - Body ground and other terminals Always 10 kΩ or higher

      HINT: 

      If a short is detected in any of the above circuits, there may be a malfunction in the circuit of a connected ECU.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. CHECK TERMINAL VOLTAGE (POWER SOURCE OF IGP RELAY) 
    1. Remove the IGP relay from the No. 1 engine room relay block and No. 1 junction block assembly.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      5 (IGP relay) - Body ground Always 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AUXILIARY BATTERY -IGP RELAY) 

    Result: 

    OK 

    See step  9

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

      Standard Resistance

      Tester Connection Condition Specified Condition
      1 (IGP relay) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  10

  10. CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - IGP RELAY) 
    1. Disconnect the certification ECU (smart key ECU assembly) connector.
    2. Remove the IGP relay from the No. 1 engine room relay block and No. 1 junction block assembly.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      K23-24 (IGPD) - 2 (IGP relay) Always Below 1 Ω
      K23-24 (IGPD) or 2 (IGP relay) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    GO TO ENTRY AND START SYSTEM (FOR START FUNCTION) 

    Refer to HOW TO PROCEED WITH TROUBLESHOOTING [12/2022 - ]

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

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.