Inspection Procedure 1: M.U.T.-III cannot communicate with electric power steering system <ECU power supply circuit system check>.


COMMENTS ON TROUBLE SYMPTOM
If the M.U.T.-III 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 EPS-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 EPS-ECU and the ETACS-ECU, the fusible link or loose connector contact
    • Open circuit between the body earth and the EPS-ECU or loose connector contact
  • Malfunction of the ETACS-ECU
  • Malfunction of the EPS-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics
Use M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?
Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).

STEP 2. Voltage measurement at the EPS-ECU connector (IG1, +BB, GND terminal)
(1) Measure the EPS-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 EPS-ECU connector (IG1 terminal) and the EPS-ECU connector (GND terminal) or body earth.
OK: Approximately system voltage
(4)Measure the voltage between the EPS-ECU connector (+BB terminal) and the EPS-ECU connector (GND terminal) or body earth.
OK: Approximately system voltage

Q. Is the check result normal?
Go to Step 5.
Go to Step 3.

STEP 3. Check of short to power supply, short to earth, and open circuit in +BB line between fusible link and EPS-ECU connector

Q. Is the check result normal?
Go to Step 4.
Repair the fusible link, connector(s) or wiring harness.

STEP 4. Check of short to power supply, short to earth, and open circuit in IG1 line between EPS-ECU connector and ETACS-ECU connector

Q. Is the check result normal?
Go to Step 5.
Repair the connector(s) or wiring harness.

STEP 5. Retest the system

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
Replace the EPS-ECU (Refer to ).