Code No. U0121:
ABS/ASC 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 - CAN Bus Diagnostics Table
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- If diagnosis code U0121 is set in electric parking brake 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 ECU is replaced, ensure that the CAN bus lines are normal.
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OPERATION
The electric parking brake ECU communicates with the ASC-ECU via the CAN bus lines.
DIAGNOSIS CODE SET CONDITIONS
If the ECU cannot receive any signal from the ASC-ECU via CAN for at least one second,
this diagnosis code will be set.
PROBABLE CAUSES
- The CAN bus line is defective.
- Power supply circuit for the ASC-ECU fails
- Malfunction of the ASC-ECU
- Malfunction of the electric parking brake ECU
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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. U0121 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 whether an ASC "time-out" related diagnosis code is set in other ECUs (Refer to
GROUP 54C - CAN-Related Diagnosis Code Table ).
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Q.
Is the diagnosis code set?
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Go to Step 4.
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Go to Step 5.
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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.
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(1)Erase the diagnosis code.
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(2)Turn the ignition switch to the LOCK (OFF) position.
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(3)Turn the ignition switch to the ON position.
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(4)Check if the diagnosis code is set.
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Q.
Is diagnosis code No. U0121 set?
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Replace the hydraulic unit (ASC-ECU) (Refer to GROUP 35C - Hydraulic
Unit).
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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 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)Erase the diagnosis code.
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(2)Turn the ignition switch to the LOCK (OFF) position.
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(3)Turn the ignition switch to the ON position.
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(4)Check if the diagnosis code is set.
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Q.
Is diagnosis code No. U0121 set?
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Replace the electric parking brake ECU (Refer to ).
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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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