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

OPERATION

The battery voltage is applied to the diagnosis connector (terminal No. 16) and is earthed to the vehicle body from the diagnosis connector (terminal No. 4 and No. 5).

COMMENT ON TROUBLE SYMPTOM

If the M.U.T.-III cannot communicate with the engine-ECU system, the CAN bus lines may be defective. If the engine-ECU system dose not work, the engine-ECU or its power supply circuit may be defective. This symptom also appears when an incorrect vehicle model is selected on the M.U.T.-III.

PROBABLE CAUSES

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

DIAGNOSIS PROCEDURE

STEP 1. Check V.C.I. operation.

Connect the M.U.T.-III to the diagnosis connector.
Ignition switch: ON
When the V.C.I. is energised, the V.C.I. indicator lamp should be illuminate in a green colour.

OK: The V.C.I. indicator lamp illuminates in a green colour.

Q. Is the check result normal?

Go to Step 6 .

Go to Step 2 .

STEP 2. Check battery voltage.

Measure battery voltage during cranking.

OK: 8 V or more

Q. Is the check result normal?

	Go to Step 3 .

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

STEP 3. Connector check: B-16 diagnosis connector

Q. Is the check result normal?

Go to Step 4 .

Repair or replace the connector.

STEP 4. Perform voltage measurement at B-16 diagnosis connector.

Voltage between terminal No. 16 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 5 .

Check power supply line for open/short circuit.

STEP 5. Perform resistance measurement at B-16 diagnosis connector.

Resistance between terminal No. 4 and earth, also between terminal No. 5 and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Refer to M.U.T.-III User’ s Manual - Troubleshooting Procedures.

Check and repair harness between B-16 (terminal No. 4) diagnosis connector and body earth.
Check and repair harness between B-16 (terminal No. 5) diagnosis connector and body earth.

Check earthing line for open circuit and damage

STEP 6. M.U.T.-III CAN bus diagnosis

warning

Since the cooling fan rotates during CAN bus line diagnostics, make sure that no one is servicing the engine compartment before diagnosing the CAN bus line. Since the CAN communication stops when diagnosing the CAN bus line, the ETACS-ECU detects the time-out of the engine-ECU, and activates the cooling fan to prevent overheating as fail-safe.

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

Q. Is the check result normal?

	Check engine-ECU power supply, engine control relay and ignition switch IG1 system (Refer to Inspection Procedure 21 ).

	Correct CAN bus line (Refer to GROUP 54C - Troubleshooting - Can Bus Diagnosis Table ).