Inspection Procedure 16: Engine-ECU Power Supply System




OPERATION



  • When the ignition switch ON signal is input to the engine-ECU, the engine-ECU places the engine control relay in the ON position. Accordingly, the battery voltage is supplied to the engine-ECU, sensor and actuator.

PROBABLE CAUSES



  • Failed battery
  • Failed ignition switch
  • Failed engine control relay
  • Damaged harness (Open circuit between engine-ECU and engine control relay, engine control relay and relay box, engine-ECU and earth, and open circuit between engine-ECU and J/B)
  • Damaged connector (Engine-ECU connector, diagnosis connector)
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check battery voltage.

  • Measure battery voltage during cranking.
OK: 8 V or more

Q. Is the check result normal?
Go to Step 2 .
Check battery (Refer to GROUP 54A - Battery - On-vehicle Service - Battery test ).

STEP 2. Check engine control relay itself.

  • Check engine control relay itself (Refer to ).

Q. Is the check result normal?
Go to Step 3 .
Replace the engine control relay.

STEP 3. Connector check: A-20X engine control relay connector.

Q. Is the check result normal?

Go to Step 4 .

Repair or replace.

STEP 4. Perform voltage measurement at A-20X engine control relay connector.


    Remove relay, and measure at harness side.
    Voltage between terminal No. 1 and earth, also between terminal No. 4 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 5 .


    Check intermediate connector A-115, and repair if necessary. If intermediate connector is normal, check and repair harness between A-20X (terminal No. 1 and terminal No. 4) engine control relay connector and battery.

STEP 5. Connector check: C-103 engine-ECU connector.

Q. Is the check result normal?

Go to Step 6 .

Repair or replace.

STEP 6. Perform voltage measurement at C-103 engine-ECU connector


  • Disconnect connector, and measure at harness side.
  • Voltage between terminal No. 109 and earth.
OK: System voltage.

Q. Is the check result normal?

Go to Step 7 .

Repair the harness wire.

STEP 7. Perform voltage measurement at C-103 engine-ECU connector.


  • Disconnect connector, and measure at harness side.
  • Short-circuit terminal No. 109 to earth.
  • Voltage between terminal No. 99 and earth also between terminal No. 100 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 8 .

Repair the harness wire.

STEP 8. Check for open circuit between engine-ECU connector C-103 and earth.


  • Disconnect connector and measure at harness side.
  • Check open circuit between terminal No. 128 and earth.

Q. Is the check result normal?

Go to Step 9 .

Repair the harness wire.

STEP 9. Connector check: C-105 engine-ECU connector.

Q. Is the check result normal?

Go to Step 10 .

Repair or replace.

STEP 10. Check for open circuit between engine-ECU connector C-105 and earth.


  • Disconnect connector.
  • Check open circuit between terminal No. 22 and earth also between terminal No. 61 and earth.

Q. Is the check result normal?

Go to Step 11 .

Repair the harness wire.

STEP 11. Perform voltage measurement at C-103 engine-ECU connector.


  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 92 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 12 .

Check intermediate connector C-53 <L.H. drive vehicles> C-35 <R.H. drive vehicles>, and repair if necessary. If intermediate connector is normal, check and repair harness between C-103 (terminal No. 92) engine-ECU connector and C-208 J/B connector.

STEP 12. Check the trouble symptoms.

Q. Does trouble symptom persist?
Replace the engine-ECU. When the engine-ECU is replaced, write the chassis number (Refer to GROUP 00 - How to Perform Chassis Number Writing ). After replacing the engine-ECU, register the injector identification code and learn fuel injection (Refer to GROUP 00 - Precautions Before Service - What The Common Rail Engine Learns ).
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).