Inspection Procedure 1: Communication with engine-A/T-ECU is not possible






OPERATION



  • The battery voltage is applied to the diagnosis connector (terminal No. 16) and is earthed to the vehicle body from the diagnosis connector (terminal No. 4 and No. 5).

COMMENT ON TROUBLE SYMPTOM



  • If the M.U.T.-III cannot communicate with the engine-A/T-ECU system, the CAN bus lines may be defective. If the engine-A/T-ECU system dose not work, the engine-A/T-ECU or its power supply circuit may be defective. This symptom also appears when an incorrect vehicle model is selected on the M.U.T.-III.

PROBABLE CAUSES



  • Open or shorted diagnosis connector circuit, harness damage, or connector damage
  • Failed CAN
  • Failed M.U.T.-III
  • Failed engine-A/T-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check engine start-up.

  • Connect the M.U.T.-III to the diagnosis connector.
  • Ignition switch: ON
  • When the V.C.I. is energised, the V.C.I. indicator lamp should be illuminate in a green colour.
OK: The V.C.I. is indicator lamp illuminates in a green colour.

Q. Is the check result normal?
Go to Step 6 .
Go to Step 2 .

STEP 2. Check battery voltage.

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

Q. Is the check result normal?
Go to Step 3 .
Check battery (Refer to GROUP 54A - Battery - On-vehicle Service - Battery Test ).

STEP 3. Connector check: D-127 diagnosis connector

Q. Is the check result normal?
Go to Step 4 .
Repair or replace the connector.

STEP 4. Perform voltage measurement at D-127 diagnosis connector.

  • Voltage between terminal No. 16 and earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 5 .

    Check intermediate connectors D-240, D-404 and D-405, and repair if necessary. If intermediate connectors are normal, check and repair harness between D-127 (terminal No. 16) diagnosis connector and battery.

    • Check power supply line for open/short circuit.

STEP 5. Perform resistance measurement at D-127 diagnosis connector.

  • Resistance between terminal No. 4 and earth, also between terminal No. 5 and earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?
Refer to M.U.T.-III Reference Manual - Troubleshooting Procedures.

    Check and repair harness between diagnosis connector and body earth.

  1. Check and repair harness between D-127 (terminal No. 4) diagnosis connector and body earth.
  2. Check and repair harness between D-127 (terminal No. 5) diagnosis connector and body earth.

  • Check earthing line for open circuit and damage

STEP 6. M.U.T.-III CAN bus diagnosis

  • Using M.U.T.-III, perform CAN bus line diagnosis.

Q. Is the check result normal?
Check engine-A/T-ECU power supply, engine control relay and ignition switch IG1 system (Refer to Inspection Procedure 19 ).
Correct CAN bus line (Refer to GROUP 54D - Troubleshooting - Can Bus Diagnosis Table ).