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DTC U0121: ASC Time-out Error
 
 
caution
  • If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines.
  • Whenever the ECU is replaced, ensure that the CAN bus lines are normal.
 
 
OPERATION
AWC-ECU communicates with the ASC-ECU via the CAN bus lines.
 
 
DTC SET CONDITIONS
The DTC is set when the signal sent from the ASC-ECU cannot be received for a certain period.
 
 
PROBABLE CAUSES
  • Malfunction of the CAN bus line
  • Malfunction of power supply circuit system (ASC-ECU)
  • Malfunction of ASC-ECU
  • Malfunction of AWC-ECU

 
 
DIAGNOSIS
STEP 1. Scan tool (M.U.T.-IIISE) CAN bus diagnostics.
Use scan tool (M.U.T.-IIISE) to perform the CAN bus diagnosis.
Is the check result normal?
Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C - Diagnosis, Can Bus Diagnostics Table ).
 
STEP 2. Check for DTC of other systems.
Check whether an ASC "time-out" related DTC is set in other ECUs (Refer to GROUP 54C - CAN-Related Diagnostic Trouble Code Table ).
Is the DTC set?
Go to Step 3.
Go to Step 4.
 
STEP 3. Check whether the DTC is set again.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the LOCK (OFF) position.
(3) Turn the ignition switch to the ON position.
(4) Check if the DTC is set.
Is the DTC U0121 set?
Replace the hydraulic unit (ASC-ECU) (Refer to GROUP 35C - Hydraulic Unit ).
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
 
STEP 4. Check whether the DTC is set again.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the LOCK (OFF) position.
(3) Turn the ignition switch to the ON position.
(4) Check if the DTC is set.
Is the DTC U0121 set?
Replace the AWC-ECU (Refer to ).
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).