Code No. U0401:
Engine ECU (CAN message)
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- If there is any
problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis,
diagnose the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table
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- Whenever ECU is replaced, ensure that the CAN bus lines are normal.
- When the hydraulic unit (integrated with ASTC-ECU) is replaced, always carry out
the calibration of the steering wheel sensor and the G and yaw rate sensor (Refer to ).
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OPERATION
Engine-related signals are sent or received to and from between ASTC-ECU and engine ECU
via CAN bus lines.
DIAGNOSIS CODE SET CONDITIONS
This diagnosis code is set when the engine ECU malfunction has been detected.
PROBABLE CAUSES
Current trouble
- Malfunction of engine system
- Malfunction of engine-ECU
- Malfunction of the hydraulic unit assembly (integrated with ASTC-ECU)
- Noise interference
Past trouble
- Carry out diagnosis with particular emphasis on wiring harness and
connector failures between ASTC-ECU and the wheel speed sensor. For diagnosis procedures, refer
to How to treat past trouble (GROUP 00 - How to Cope with Intermittent Malfunctions ).
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STEP 1. M.U.T.-III CAN bus diagnosis
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Use the 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 3.
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 Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
On completion, go to Step 2.
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STEP 2. Diagnosis code recheck after resetting CAN bus lines
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Q.
Is diagnosis code No. U0401 set?
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Go to Step 3.
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This diagnosis is complete.
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STEP 3. Check for diagnosis codes of other systems.
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Check if diagnosis code(s) other than U0401 is set.
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Q.
Is the diagnosis code set?
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Follow the relevant diagnosis code procedure, and then go to Step 6.
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Go to Step 4.
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STEP 4. Use M.U.T.-III to confirm a diagnosis code of other systems.
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Check if the diagnosis code is set in the engine ECU (Refer to GROUP 13C - Diagnosis
Code Chart ).
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Q.
Is the diagnosis code set?
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Troubleshoot the engine ECU diagnosis code (Refer to GROUP 13C - Diagnosis
Code Chart ). Then go to Step 6.
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Go to Step 5.
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STEP 5. Check whether the diagnosis code is set again.
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Check again if the diagnosis code is set.
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(1)Turn the ignition switch to the "LOCK" (OFF) position.
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(2)Turn the ignition switch to the "ON" position.
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(3)Erase the diagnosis code.
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(4)Turn the ignition switch to the "LOCK" (OFF) position.
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(5)Turn the ignition switch to the "ON" position.
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(6)Check if the diagnosis code is set.
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Q.
Is diagnosis code No. U0401 set?
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Replace the hydraulic unit assembly (integrated with ASTC-ECU). (Refer to .)
Then go to Step 6.
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The trouble can be an intermittent malfunction (Refer to GROUP 00 - How
to Cope with Intermittent Malfunction ).
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STEP 6. Check whether the diagnosis code is set again.
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Check again if the diagnosis code is set.
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(1)Turn the ignition switch to the "LOCK" (OFF) position.
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(2)Turn the ignition switch to the "ON" position.
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(3)Erase the diagnosis code.
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(4)Turn the ignition switch to the "LOCK" (OFF) position.
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(5)Turn the ignition switch to the "ON" position.
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(6)Check if the diagnosis code is set.
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Q.
Is diagnosis code No. U0401 set?
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Return to Step 1.
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The procedure is complete.
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