Inspection Procedure 1: The Communication Between M.U.T.-III and AS&G-ECU Not Possible

OPERATION

The battery voltage is supplied to the diagnosis connector from the ETACS-ECU connector terminal MUT.
The diagnosis connector earth terminals are earthed to the vehicle body.

COMMENT ON TROUBLE SYMPTOM

When the communication between M.U.T.-III and the AS&G-ECU is impossible, the CAN bus line, power supply circuit of the diagnosis connector, and/or earthing circuit could possibly be defective. The communication cannot be achieved either if the wrong vehicle type is selected on M.U.T.-III.

PROBABLE CAUSES

Open/short circuit or harness damage in the diagnosis connector circuit or loose connector contact
Failed CAN communication
Failed M.U.T.-III
Failed ETACS-ECU
Failed AS&G-ECU

DIAGNOSIS PROCEDURE

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

Connect the M.U.T.-III to the diagnosis connector.
Turn ON the power of the Vehicle Communication Interface (V.C.I.).

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 battery.

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

Q. Is the check result normal?

	Go to Step 3.

	Replace the battery.

STEP 3. Perform voltage measurement at diagnosis connector.

Voltage between terminal ETACS-ECU MUT line and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 5.

	Go to Step 4.

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

Q. Is the check result normal?

	Check ETACS-ECU power supply circuit (Refer to GROUP 54A - ETACS - Symptom Procedures - Malfunction of ETACS-ECU Power Supply Circuit ).

	Repair the connector(s) or wiring harness.

STEP 5. Perform resistance measurement at diagnosis connector.

Resistance between earth and body earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

	Go to Step 6.

	Repair the connector(s), or check of open circuit, and harness damage in earthing line between diagnosis connector and body earth.

STEP 6. Check of harness 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 7. M.U.T.-III CAN bus diagnosis

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

Q. Is the check result normal?

	Check AS&G-ECU Power Supply, Ignition Switch-IG1 System (Refer to ).

	Repair CAN bus line (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnostics Table ).