Code No. C121C Torque request signal denied


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 - CAN Bus Diagnostics Table ).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.

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

DIAGNOSIS CODE SET CONDITIONS
This diagnosis code is set when the request for the decrease of output is rejected by the engine ECU.

PROBABLE CAUSES

  • Wrong coding of engine ECU
  • Engine ECU malfunction
  • ASC-ECU malfunction
  • External noise interference

DIAGNOSTIC PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnosis
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 Diagnostics Table ). On completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting CAN bus lines

Q. Is diagnosis code No.C121C set?
Go to Step 3
This diagnosis is complete.

STEP 3. M.U.T.-III other system diagnosis code
Use M.U.T.-III to check that the diagnosis code is set in the engine ECU.

Q. Is the diagnosis code set?
Troubleshoot the engine ECU diagnosis code (Refer to GROUP 13A - Troubleshooting/Diagnosis function <4B1> or GROUP 13C - Troubleshooting/Diagnosis function <4J1> or GROUP 13D - Troubleshooting/Diagnosis function <4N1>), and then go to Step 7.
Go to Step 4

STEP 4. M.U.T.-III diagnosis code
Check that diagnosis code No.C1707 is set in ASC-ECU.

Q. Is diagnosis code No.C1707 set?
Troubleshoot for diagnosis code No.C1707 (Refer to ). Then go to Step 5.
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ). Then go to Step 7.

STEP 5. M.U.T.-III data list
Check the following service data (Refer to ).

  • Item 68: Allow ESP torque request

Q. Is the check result normal?
Go to Step 6
Replace the engine ECU (Refer to GROUP 13A - Engine-ECU <4B1>, GROUP 13C - Engine-ECU <4J1>, GROUP 13D - Engine-ECU <4N1>), and then go to Step 7.

STEP 6. Check whether the diagnosis code is reset.
Erase the diagnosis code.

Q. Is diagnosis code No.C121C set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ). Then go to Step 7.
If the trouble symptom is resolved, an intermittent malfunction such as poorly engaged connector(s) or wiring harness is suspected (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions ).

STEP 7. Diagnosis code recheck
Erase the diagnosis code.

Q. Is diagnosis code No.C121C set?
Return to Step 1.
This diagnosis is complete.