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 10.
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. Perform voltage measurement at diagnosis connector (power supply line)


(1)Check the voltage between the diagnosis connector (power supply line) and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 6.
Go to Step 4.

STEP 4. Check of short to earth, and open circuit in MUT line between ETACS-ECU connector and diagnosis connector.


Q. Is the check result normal?

Go to Step 5.
Repair the connector(s) or wiring harness.

STEP 5. Check of short to earth, and open circuit in +B1 line between auxiliary battery and ETACS-ECU connector.


Q. Is the check result normal?

Check fuse in the ETACS-ECU, and replace if necessary. If the fuse is normal, replace the ETACS-ECU.
Repair the connector(s) or wiring harness.

STEP 6. Resistance measurement at diagnosis connector (body earth line).


(1)Check the resistance between the diagnosis connector (body earth line) and body earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 7.

    Repair body earth line between the diagnosis connector and body earth.

STEP 7. Continuity check on ETACS-ECU connectors


(1)Disconnect the connector, and measure at the ETACS-ECU side.
(2)Continuity check between the ETACS-ECU connector (+B1 terminal) and the ETACS-ECU connector (MUT terminal).
OK: Continuity

Q. Is the check result normal?

Go to Step 8.
Check fuse in the ETACS-ECU, and replace if necessary. If the fuse is normal, replace the ETACS-ECU.

STEP 8. Check of damage in +B1 line between battery and ETACS-ECU connector.


Q. Is the check result normal?

Go to Step 9.
Repair the connector(s) or wiring harness.

STEP 9. Check of damage in MUT line between ETACS-ECU connector and diagnosis connector.


Q. Is the check result normal?

Refer to the M.U.T.-III reference manual.
Repair the connector(s) or wiring harness.

STEP 10. M.U.T.-III CAN bus diagnosis



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

Q. Is the check result normal?

Check Inspection Procedure - BMU power supply system (Refer to ).
Perform troubleshooting for CAN (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnostics Table ).