Inspection Procedure 1: The Communication Between M.U.T.-III and Engine-ECU is Not Possible

OPERATION

Battery voltage is applied to the diagnosis connector.
The diagnosis connector is earthed to the vehicle body.

COMMENTS ON TROUBLE SYMPTOM

When the communication between M.U.T.-III and the engine-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

Defective diagnosis connector.
Open/short circuit or harness damage in diagnosis connector circuit or loose connector contact.
Defective CAN communication.
Defective M.U.T.-III.
Failed engine-ECU

DIAGNOSIS PROCEDURE

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

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

OK: The indicator lamp of the Vehicle Communication Interface (V.C.I.) illuminates in green.

Q. Is the check result normal?

	Go to Step 6.

	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 and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector(s), or check and repair the harness of open circuit, and short circuit in power supply line between diagnosis connector and battery.

STEP 4. Perform resistance measurement at diagnosis connector.

Resistance between terminal earth lines and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

	Go to Step 5.

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

STEP 5. Check of damage in power supply line between diagnosis connector and battery.

Q. Is the check result normal?

	Go to Step 6.

	Repair the connector(s) or wiring harness.

STEP 6. 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 - engine-ECU power supply, engine control relay, ignition switch-IG1 system (Refer to ).

	Perform troubleshooting for CAN (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnostics Table ).