Code No. C121A Abnormality in steering wheel sensor calibration


caution
  • 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, Trouble code diagnosis ).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.
  • When the steering wheel sensor is replaced, always carry out calibration to make ASC-ECU learn the neutral point (Refer to ).
  • When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out the calibration of the steering wheel sensor, the G and yaw rate sensor and brake fluid pressure sensor (Refer to , and ).

OPERATION
Steering wheel sensor stores the neutral position learned by M.U.T.-III. 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.

DIAGNOSIS CODE SET CONDITIONS
This diagnosis code is set when ASC-ECU detects that the steering wheel sensor has not learned the neutral position yet.

PROBABLE CAUSES

  • Neutral position of steering wheel sensor not learned
  • Steering wheel sensor malfunction
  • ASC-ECU malfunction

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics
Use M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?
Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnosis table ). On completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting CAN bus lines

Q. Is diagnosis code No.C121A set?
Go to Step 3.
This diagnosis is complete.

STEP 3. Steering wheel sensor calibration
Perform calibration of steering wheel sensor (Refer to ).

Q. Has the calibration succeeded?
Go to Step 4.
After the steering wheel sensor is replaced, perform the steering wheel sensor calibration to make ASC-ECU learn the neutral point again (Refer to ). Then go to Step 4.

STEP 4. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.C121A set?
Replace the hydraulic unit (ASC-ECU) (Refer to ), and then go to Step 5.
This diagnosis is complete.

STEP 5. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.C121A set?
Return to Step 1.
This diagnosis is complete.