Inspection Procedure 1: Communication with Engine-ECU is Not Possible

OPERATION

Battery voltage is applied to the diagnosis connector terminal.
The diagnosis connector terminal 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 10.

	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 body earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 6.

	Go to Step 4.

STEP 4. Continuity check on ETACS-ECU connectors

Disconnect connectors, and measure at the ETACS-ECU side.
Continuity check between terminal +B1 and MUT

OK: Continuity

Q. Is the check result normal?

	Go to Step 5.

	Repair or replace the connector, or check fuse in the ETACS-ECU, and replace if necessary. If the fuse is normal, replace the ETACS-ECU.

STEP 5. Check harness between the battery and ETACS-ECU connector terminal +B1.

Check power supply line for open/short circuit.

Q. Is the check result normal?

	Repair or replace the connector, or check and repair the harness between ETACS-ECU connector terminal MUT and diagnosis connector terminal. Check power supply line for open/short circuit.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 6. Perform resistance measurement at diagnosis connector.

Resistance between terminal earthing lines and body earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

	Go to Step 7.

	Repair or replace the connector, or check and repair the harness between the diagnosis connector terminal and body earth. Check earthing line for open circuit and damage.

STEP 7. Continuity check on ETACS-ECU connectors

Disconnect connectors, and measure at the ETACS-ECU side.
Continuity check between terminal +B1 and MUT

OK: Continuity

Q. Is the check result normal?

	Go to Step 8.

	Repair or replace the connector, or check fuse in the ETACS-ECU, and replace if necessary. If the fuse is normal, replace the ETACS-ECU.

STEP 8. Check harness between the battery and ETACS-ECU connector terminal +B1.

Check power supply line for damage.

Q. Is the check result normal?

	Go to Step 9.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 9. Check harness between ETACS-ECU connector terminal MUT and diagnosis connector terminal.

Check power supply line for damage.

Q. Is the check result normal?

	Refer to the M.U.T.-III reference manual.

	Repair or replace the connector, or repair the damaged harness wire.

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 engine-ECU power supply system (Refer to ).

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