Inspection Procedure 1: Scan tool cannot communicate with electric power steering system < ECU power supply circuit system check >: 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?
1. YES: Go to Step 2.
2. NO: Repair the CAN bus lines (Refer to CAN BUS DIAGNOSTICS TABLE ).
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?
1. YES: Go to Step 3.
2. 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?
1. YES: Go to step 4.
2. 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?
1. YES: Go to Step 5.
2. NO: Check the fusible link or the ETACS-ECU and repair if necessary (Refer to ETACS-ECU ).
  
  Fig 1: Measuring Voltage Between C-309 ETACS-ECU Connector Terminal No. 1 And C-317 ETACS-ECU Connector Terminal No. 5
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
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?
1. YES: Go to Step 6
2. NO: Check the fusible link or the ETACS-ECU and repair if necessary (Refer to ETACS-ECU ).
  
  Fig 2: Measuring Voltage Between C-141 Electric Power Steering-ECU Connector Terminals No. 1 And C-140 Electric Power Steering-ECU Connector Terminal No. 12
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  
  Fig 3: Measuring Voltage Between C-140 Electric Power Steering-ECU Connector Terminals No. 11 And No. 12
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
STEP 6. Retest the system
Q: Is the check result normal?
1. YES: Intermittent malfunction (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS ).
2. NO: Replace the electric power steering-ECU (Refer to ELECTRIC POWER STEERING CONTROL UNIT (EPS-ECU) ).