C121C

DTC C121C Torque request signal rejection

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 (Refer to Diagnostic trouble code diagnosis Diagnostic Trouble Code Descriptions).
^ 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.
^ 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.

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

DTC SET CONDITIONS
This DTC is set when the request for the decrease of output is rejected by the engine control module (ECM).

PROBABLE CAUSES
^ Wrong coding of engine control module (ECM)
^ engine control module (ECM) malfunction
^ ASC-ECU malfunction
^ External noise interference

DIAGNOSTIC PROCEDURE

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 (Refer to Diagnosis - CAN Bus Diagnostic Table CAN Bus Diagnostics Table). On completion, go to Step 2.

STEP 2. DTC recheck after resetting CAN bus lines
Q: Is DTC C121C set?
YES: Go to Step 3.
NO: The procedure is complete.

STEP 3. Using scan tool MB991958, check the other system DTC
Use scan tool to check that the DTC is set in the engine control module (ECM).
Q: Is the DTC set?
YES: Troubleshoot the engine control module (ECM). (Refer to Troubleshooting Diagnosis function Testing and Inspection [2.0L engine non-turbo][2.0L engine turbo][2.4L engine]), and then go to Step 7.
NO: Go to Step 4.

STEP 4. Using scan tool MB991958, check the DTC
Check that DTC U1417 is set in ASC-ECU.
Q: Is DTCU1417 set?
YES: Troubleshoot for DTC U1417 (Refer to U1417). Then go to Step 5.
NO: Replace the hydraulic unit (ASC-ECU). Then go to Step 7.

STEP 5. Using scan tool MB991958, check the data list
Check the following service data (Refer to Scan Tool Testing and Procedures).
^ Item 68: Allow ESP torque request
Q: Is the check result normal?
YES: Go to Step 6.
NO: Replace the engine control module (ECM) (Refer to Troubleshooting Diagnosis function Testing and Inspection [2.0L engine non-turbo][2.0L engine turbo][2.4L engine]), and then go to Step 7.

STEP 6. Check whether the DTC is reset.
Q: Is DTC C121C set?
YES: Replace the hydraulic unit (ASC-ECU). Then go to Step 7.
NO: If the trouble symptom is resolved, an intermittent malfunction such as poorly engaged connector(s) or wiring harness is suspected.

STEP 7. Check whether the DTC is reset
Q: Is DTC C121C set?
YES: Return to Step 1.
NO: The procedure is complete.