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 CAN Bus Line Diagnostics 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 Active Stability Control System (ASC)).
- 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 Active Stability Control System (ASC), Active Stability Control System (ASC) and Active Stability Control System (ASC)).

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

DIAGNOSIS

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 CAN Bus Diagnostics Chart).
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) Multiport Fuel Injection (MFI), Diagnosis/Diagnostic Trouble Code Chart Multiport Fuel Injection (MFI) Multiport Fuel Injection (MFI), 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 Active Stability Control System (ASC)). Then go to Step 5.
NO Replace the hydraulic unit (ASC-ECU) (Refer to Active Stability Control System (ASC)).
Then go to Step 7.
STEP 5. Using scan tool MB991958, check the 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 6.
NO Replace the engine control module (ECM) Removal and Replacement Removal and Replacement Removal and Replacement, and then go to Step 7.
STEP 6. 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 Active Stability Control System (ASC)).
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 How to Cope With Intermittent Malfunctions).
STEP 7. Check whether the DTC is reset

Erase the DTC.

Q. Is DTC C121C set?

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