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DTC C121A SAS Initialization
 
 
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 (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.
  • When the column switch assembly (integrated with steering wheel sensor) is replaced, always carry out calibration to make ASC-ECU learn the neutral point (Refer to ).
 
 
OPERATION
Steering wheel sensor stores the neutral position learned by scan tool (M.U.T.-IIISE). When the neutral position has not been stored in the steering wheel sensor yet, the steering wheel sensor outputs the signal indicating that it does not have neutral position.
 
 
 
DTC SET CONDITIONS
This DTC is set when ASC-ECU detects that the steering wheel sensor has not learned the neutral position yet.
 
 
 
PROBABLE CAUSES
  • CAN bus lines are abnormal (External noise interference)
  • Neutral position of steering wheel sensor not learned
  • Column switch assembly (integrated with steering wheel sensor) malfunction
  • ASC-ECU malfunction
 
 
 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-IIISE), diagnose the CAN bus line.
Use scan tool (M.U.T.-IIISE) to diagnose the CAN bus lines.
Is the check result normal?
Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
 
STEP 2. Check for column switch assembly (integrated with steering wheel sensor) installation.
Refer to GROUP 54A - Column Switch .
Is the check result normal?
Go to Step 3.
Repair it.
 
STEP 3. Steering wheel sensor calibration.
Perform calibration of steering wheel sensor (Refer to ).
Has the calibration succeeded?
Go to Step 4.
After the column switch assembly (integrated with steering wheel sensor) is replaced (Refer to GROUP 54A - Column Switch ), perform the steering wheel sensor calibration to make ASC-ECU learn the neutral point again (Refer to ).
 
STEP 4. Check whether the DTC is set again.
(1) Turn the ignition switch to the "LOCK" (OFF) position.
(2) Turn the ignition switch to the "ON" position.
Is DTC C121A set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ).
This diagnosis is complete.