Code No. C121C Torque request signal rejection


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 Diagnosis Table ).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.
  • Do not drop or shock the G and yaw rate sensor.
  • When the G and yaw rate 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
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

DIAGNOSIS 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 Diagnosis 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 (Refer to GROUP 13A - Troubleshooting, Diagnosis function <1500> or GROUP 13B - Troubleshooting, Diagnosis function <PETROL (1800, 2000: except 2000-T/C)> or GROUP 13F - Troubleshooting, Diagnosis function <DIESEL> or GROUP 13E - Troubleshooting, Diagnosis function <PETROL(2000 - T/C)>), and then go to Step 7.
Go to Step 4.

STEP 4. M.U.T.-III diagnosis code
Check that diagnosis code No.U1417 is set in ASC-ECU.

Q. Is diagnosis code No.U1417 set?
Troubleshoot for diagnosis code No.U1417 (Refer to ). Then go to Step 5.
Replace the 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 - Troubleshooting, Diagnosis function <1500> or GROUP 13B - Troubleshooting, Diagnosis function <1800, 2000: except 2000-T/C> or GROUP 13F - Troubleshooting, Diagnosis function <DIESEL> or GROUP 13E - Troubleshooting, Diagnosis function <PETROL(2000 - T/C)>), and then go to Step 7.

STEP 6. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.C121C set?
Replace the hydraulic unit (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 Cope with Intermittent Malfunction ).

STEP 7. Diagnosis code recheck

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