Code No. U0121:
ASTC CAN Timeout
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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 - Troubleshooting
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- If diagnosis code No. U0121 is set in ACC/FCM-ECU, always diagnose the CAN bus line. If
there is any fault in the CAN bus lines, an incorrect diagnosis code may be set. In this case,
the set diagnosis code is not highly reliable.
- Whenever the ECU is replaced, ensure that the CAN bus lines are normal.
- When the hydraulic unit assembly (integrated with ASTC-ECU) is replaced, always
carry out the calibration of the steering wheel sensor and the G sensor (Refer to GROUP 35C - On-vehicle
Service).
- When the ACC/FCM-ECU is replaced, calibrate the radar (refer to ).
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OPERATION
The ACC/FCM-ECU communicates with the ASTC-ECU via the CAN bus lines.
DIAGNOSIS CODE SET CONDITION
The ACC/FCM-ECU receives the ASTC system-related signals from the ASTC-ECU via
the CAN bus lines. When these signals cannot be received, the ECU sets this diagnosis code.
PROBABLE CAUSES
- Malfunction of the CAN bus line
- Malfunction of the hydraulic unit assembly (integrated with ASTC-ECU)
- Malfunction of the ACC/FCM-ECU
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STEP 1. M.U.T.-III CAN bus diagnostics.
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Use M.U.T.-III to perform the CAN bus diagnosis.
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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 - Troubleshooting ).
On completion, go to Step 2.
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STEP 2. 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 ASTC-ECU (Refer to GROUP 35C - Troubleshooting <ASTC-ECU>,
Diagnosis Function).
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Q.
Is the diagnosis code set?
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Troubleshoot the ASTC-ECU diagnosis code (Refer to GROUP 35C - Troubleshooting <ASTC-ECU>, Diagnosis
Code Chart ).
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Go to Step 3.
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STEP 3. Use M.U.T.-III to confirm a diagnosis code of other systems.
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Check whether an ASTC-ECU "time-out" related diagnosis code is set in other ECUs.
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Q.
Is the diagnosis code set?
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Replace the hydraulic unit assembly (integrated with ASTC-ECU) (Refer to GROUP
35C - Hydraulic Unit).
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Go to Step 4.
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STEP 4. Check whether the diagnosis code is set again.
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Check again if the diagnosis code is set in the ACC/FCM-ECU.
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(1)Erase the diagnosis code.
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(2)Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
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(4)Press the ACC ON/OFF switch to turn the ACC system to ON.
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(5)On completion, check that the diagnosis code is set again.
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Q.
Is diagnosis code No. U0121 set?
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Replace the ACC/FCM-ECU (Refer to ).
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Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent
Malfunction).
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