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 junction block, the fusible
link or loose connector contact
- Open circuit between the body earth and the EPS-ECU or loose connector contact
- Malfunction of the EPS-ECU
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STEP 1. M.U.T.-III CAN bus diagnostics
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Use M.U.T.-III to diagnose the CAN bus lines.
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Q.
Is the check result normal?
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Go to Step 2.
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Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
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STEP 2. Wiring harness check
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(1)Check the wiring harness between the junction block connector terminal and the
fusible link for damage or other problem.
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(2)Check the wiring harness between the EPS-ECU connector terminal IG1 and the junction
block connector terminal for damage or other problem.
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(3)Check the wiring harness between the EPS-ECU connector terminal +BB and
the junction block connector terminal for damage or other problem.
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(4)Check the wiring harness between the EPS-ECU connector terminal GND and the body
earth point for damage or other problem.
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Q.
Is the check result normal?
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Go to step 3.
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Repair the defective connector(s) or terminal(s), or repair the defective wiring
harness.
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STEP 3. Voltage measurement at the junction block connector
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(1)Measure the junction block voltage without disconnecting the connector (by backprobing).
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(2)Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
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(3)Measure the voltage between the junction block connector terminals. OK: Approximately system voltage
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Q.
Is the check result normal?
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Go to Step 4.
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Check the fusible link or the junction block and repair if necessary.
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STEP 4. Voltage measurement at the EPS-ECU connector
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(1)Measure the EPS-ECU voltage without disconnecting the connector (by backprobing).
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(2)Turn the ignition switch from the "LOCK" (OFF) position to the "ON" position.
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(3)Measure the voltage between the EPS-ECU connector terminal IG1 and GND. OK: Approximately system voltage
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(4)Measure the voltage between the EPS-ECU connector terminals +BB and GND. OK: Approximately system voltage
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Q.
Is the check result normal?
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Go to Step 5.
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Check the fusible link or the junction block and repair if necessary.
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STEP 5. Retest the system
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Q.
Is the check result normal?
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Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent
Malfunction ).
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Replace the EPS-ECU (Refer to ).
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