Inspection Procedure 1

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Inspection Procedure 1: Scan tool cannot communicate with electric power steering system [ECU power supply circuit system check].

















COMMENTS ON TROUBLE SYMPTOM

If the scan tool cannot communicate with the electric power steering system, the CAN bus lines may be defective. If the electric power steering system does not operate, the electric power steering-ECU or its power supply may be defective.

PROBABLE CAUSES

- Malfunction of CAN bus line
- Defective harness wire(s) or connector(s)
- Short or open circuit between the electric power steering-ECU and the ETACS-ECU, the fusible link or loose connector contact
- Open circuit between the body ground and the electric power steering-ECU or loose connector contact
- Malfunction of the ETACS-ECU
- Malfunction of the electric power steering-ECU

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)

STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.

Use scan tool to diagnose the CAN bus lines.

Q. Is the check result normal?

YES Go to Step 2.
NO Repair the CAN bus lines CAN Bus Diagnostics Chart).
STEP 2. Check the following connector.

Check the connectors below for improper engagement, terminal damage or terminal drawn in the connector case.

- C-140 and C-141 electric power steering-ECU connector
- C-309 and C-317 ETACS-ECU connector
- C-128 intermediate connector
- No.34 and 35 fusible link
- Body ground point

Q. Is the connectors and terminals in good condition?

YES Go to Step 3.
NO Repair the defective connector(s) or terminal(s).
STEP 3. Wiring harness check

(1)Check the wiring harness between the C-140 electric power steering-ECU connector terminal No.11 and the fusible link No.35 for damage or other problem .

(2)Check the wiring harness between the C-141 electric power steering-ECU connector terminal No.1, the C-128 intermediate connector terminal No.19 and the C-317 ETACS-ECU connector terminal No.5 for damage or other problem .

(3)Check the wiring harness between the C-309 ETACS-ECU connector terminal No.1 and the fusible link No.34 for damage or other problem .

(4)Check the wiring harness between the C-140 electric power steering-ECU connector terminal No.12 and the body ground point for damage or other problem .

Q. Is the wiring harness in good condition?

YES Go to step 4.
NO Repair the defective wiring harness.
STEP 4. Voltage measurement at the ETACS-ECU connector





(1) Measure the ETACS-ECU voltage without disconnecting the connector (by backprobing).
(2)Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
(3)Measure the voltage between the C-309 ETACS-ECU connector terminal No.1 and the C-317 ETACS-ECU connector terminal No.5.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 5.

NO Check the fusible link or the ETACS-ECU and repair if necessary Electronic Time and Alarm Control System (ETACS)-ECU Removal and Installation).

STEP 5. Voltage measurement at the electric power steering-ECU connector









(1) Measure the electric power steering-ECU voltage without disconnecting the connector (by backprobing).
(2)Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
(3)Measure the voltage between the C-141 electric power steering-ECU connector terminal No.1 and the C-140 electric power steering-ECU connector terminal No.12.
OK: Approximately system voltage
(4)Measure the voltage between the C-140 electric power steering-ECU connector terminals No.11 and No.12.
OK: Approximately system voltage

Q. Is the check result normal?

YES Go to Step 6

NO Check the fusible link or the ETACS-ECU and repair if necessary Electronic Time and Alarm Control System (ETACS)-ECU Removal and Installation).

STEP 6. Retest the system

Q. Is the check result normal?

YES Intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace the electric power steering-ECU (Refer to Service and Repair).