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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 (Refer to GROUP 54C - CAN Bus Line Diagnostic Flow ).
  • 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 ).
 
 
CIRCUIT OPERATION
ASC-ECU sends the signal to the engine control module as necessary to decrease the engine output for the ASC system operation.
 
 
 
DTC SET CONDITIONS
This diagnostic trouble code is set when the request for the decrease of output is rejected by the engine control module.
 
 
 
PROBABLE CAUSES
  • Wrong coding
  • Engine control module malfunction
  • ASC-ECU malfunction
  • External noise interference
 
 
 
 
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.
Use scan tool to diagnose the CAN bus lines.
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. DTC recheck after resetting CAN bus lines
Is DTC C121C set?
Go to Step 3.
The procedure is complete.
 
STEP 3. M.U.T.-III other system diagnostic trouble code
Use scan tool to check that the diagnostic trouble code is set in the engine control module.
Is any DTC set?
Troubleshoot the engine control module diagnostic trouble code (Refer to GROUP 13A - Diagnostic Trouble Code Chart <2.0L Engine> or GROUP 13C - Diagnostic Trouble Code Chart <2.4L Engine>).
Go to Step 4.
 
STEP 4. M.U.T.-III diagnostic trouble code
Check that the diagnostic trouble code U1417 is set in ASC-ECU.
Is DTC U1417 set?
Troubleshoot for the diagnostic trouble code U1417 (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 data list (Refer to ).
  • Item 13: Allow A.S.C. torque request
Is the check result normal?
Go to Step 6.
Troubleshoot the engine control module diagnostic trouble code (Refer to GROUP 13A - Diagnostic Trouble Code Chart <2.0L Engine> or GROUP 13C - Diagnostic Trouble Code Chart <2.4L Engine>), and then go to Step 7.
 
STEP 6. Check whether the diagnostic trouble code is set again.
Erase the DTC.
Is DTC 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. Check whether the diagnostic trouble code is set again.
Erase the DTC.
Is DTC C121C set?
Return to Step 1.
The procedure is complete.