Active Stability Control System (ASC)

DTC C121A Abnormality in steering wheel sensor calibration

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 CAN Bus Line Diagnostics Flow.
- 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 Active Stability Control System (ASC)).
- 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 Active Stability Control System (ASC), Active Stability Control System (ASC) and Active Stability Control System (ASC)).

OPERATION

Steering wheel sensor stores the neutral position learned by scan tool. 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

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

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A

STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.

Use scan tool to diagnose the CAN bus lines.

Q. Is the check result normal?

YES Go to Step 3.
NO Repair the CAN bus lines CAN Bus Diagnostics Chart).
On completion, go to Step 2.
STEP 2. DTC recheck after resetting CAN bus lines

Q. Is DTC C121A set?

YES Go to Step 3.
NO The procedure is complete.
STEP 3. Steering wheel sensor calibration

Perform calibration of steering wheel sensor (Refer to Active Stability Control System (ASC)).

Q. Has the calibration succeeded?

YES Go to Step 4.
NO After the steering wheel sensor is replaced, perform the steering wheel sensor calibration to make ASC-ECU learn the neutral point again (Refer to Active Stability Control System (ASC)).
Then go to Step 4.
STEP 4. Check whether the DTC is reset.

Erase the DTC.

Q. Is DTC C121A set?

YES Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Active Stability Control System (ASC)), and then go to Step 5.
NO The procedure is complete.
STEP 5. Check whether the DTC is reset.

Erase the DTC.

Q. Is DTC C121A set?

YES Return to Step 1.
NO The procedure is complete.