C121C

DTC C121C: Torque request signal rejection

CAUTION:

- If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be set. Prior to this diagnosis, diagnose the CAN bus lines Initial Inspection and Diagnostic Overview ).
- Whenever the ECU is replaced, ensure that the CAN bus lines are normal.
- When the hydraulic unit (integrated with ASC-ECU) is replaced, always perform the calibration of steering wheel sensor, G and yaw rate sensor, brake fluid pressure sensor, cut valve, and inlet valve (Refer to G and Yaw Rate Sensor Calibration , Testing and Inspection , Master Cylinder Brake Fluid Pressure Sensor Calibration , and Testing and Inspection ).

CIRCUIT OPERATION

ASC-ECU sends the signal to the engine control module as necessary to decrease the engine output for ASC system operation.

DTC SET CONDITIONS

This diagnostic trouble code is set when the output decrease request is rejected by the engine control module.

PROBABLE CAUSES

- Wrong coding
- Engine ECU malfunction
- ASC-ECU malfunction
- External noise interference

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.

Using scan tool MB991958, 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.) After repairing the CAN bus line, go to Step 2.
STEP 2. DTC recheck after repairing the CAN bus line

Q. Is DTC C121C set?

YES Go to Step 3.
NO The procedure is complete.
STEP 3. M.U.T.-III other system diagnostic trouble code

Using scan tool MB991958, check if a diagnostic trouble code is set in the engine control module Multiport Fuel Injection (MFI)).

Q. Is any DTC set?

YES Troubleshoot the diagnostic trouble code of engine control module Multiport Fuel Injection (MFI)).
NO Go to Step 4.
STEP 4. Scan tool data list

Check the following data list (Refer to Data List Reference Table).

- Item 68: Allow ESP torque request

Q. Is the check result normal?

YES Go to Step 5.
NO Replace the engine control module Removal and Replacement). Then go to Step 5.
STEP 5. Check whether the DTC is reset.

Erase the DTC.

Q. Is DTC C121C set?

YES Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Service and Repair). Then go to Step 6.
NO Intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 6. Check whether the DTC is reset.

Erase the DTC.

Q. Is DTC C121C set?

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