Inspection Procedure 1: Communication between the M.U.T.-III and the BMU is not possible






COMMENT ON TROUBLE SYMPTOM

  • If the communications cannot be done between the M.U.T.-III and the BMU, the CAN bus line would be failed, the power supply circuit of the diagnosis connector would be failed and the earth circuit would be failed. If the vehicle type is not correctly selected in the M.U.T.-III, the communication would be disabled.

PROBABLE CAUSE

  • The diagnosis connector is failed.
  • Open circuits or short circuits of diagnosis connector; or poor contact of connector
  • The CAN communication is failed.
  • The M.U.T.-III is failed.
  • The BMU is failed.

DIAGNOSIS PROCEDURE

STEP 1. Check the Vehicle Communication Interface (V.C.I.) operations



  • Connect the M.U.T.-III to the diagnosis connector.
  • The power of Vehicle Communication Interface (V.C.I.) is turned to ON.
OK: The indicator lamp of the Vehicle Communication Interface (V.C.I.) illuminates in green

Q. Is the check result normal?

Go to Step 7 .

Go to Step 2 .

STEP 2. Check auxiliary battery

  • Check auxiliary battery (Refer to GROUP 54A - Auxiliary Battery - On-vehicle Service - Battery Test ).

Q. Is the check result normal?
Go to Step 3 .
Replace the auxiliary battery.

STEP 3. Connector check: B-20 diagnosis connector


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

STEP 4. Perform voltage measurement at B-20 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 B-303 and B-310, and repair if necessary. If intermediate connectors are normal, check and repair harness between B-20 (terminal No. 16) diagnosis connector and auxiliary battery.

    • Check power supply line for open circuit, short circuit to earth.

STEP 5. Perform resistance measurement at B-20 diagnosis connector



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

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

    Check intermediate connector B-11, and repair if necessary. If intermediate connector is normal, check and repair harness between B-20 (terminal No. 4 or terminal No. 5) diagnosis connector and body earth.

    • Check earthing line for open circuit and damage.

STEP 6. Check harness between auxiliary battery and B-20 (terminal No. 16) diagnosis connector
note Before checking harness, check intermediate connectors B-303, B-310, and repair if necessary.

  • Check power supply line for damage.

Q. Is the check result normal?
Refer to the M.U.T.-III reference manual.
Repair.

STEP 7. M.U.T.-III CAN bus diagnosis

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

Q. Is the check result normal?
Check on BMU power supply system (Refer to Inspection Procedure 2 ).
Perform troubleshooting for CAN (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnostics Table ).