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. 118 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. 118 to earth.
  • Voltage between terminal No. 101 and earth also between terminal No. 102 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. 145 and earth.

Q. Is the check result normal?

Go to Step 9.

Repair the harness wire.

STEP 9. Connector check: C-103 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-103 and earth.


  • Disconnect connector.
  • Check open circuit between terminal No. 116 and earth also between terminal No. 117 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. 104 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 12.

Check intermediate connector C-53 <L. H. drive vehicles> or C-35 <R. H. drive vehicles>, and repair if necessary. If intermediate connector is normal, check and repair harness between C-103 (terminal No. 104) 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 - Precautions Before Service - 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 ). After registering the injector identification code, the vehicle equipped with the DPF carries out the forcible DPF regeneration. (Refer to GROUP 17 - Emission Control - Diesel Particulate Filter (DPF) System - Forcible DPF Regeneration ).
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).