Code No.C121D Abnormality in brake fluid pressure sensor circuit

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, Trouble code diagnosis ).
Whenever ECU is replaced, ensure that the CAN bus lines are normal.
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

The hydraulic sensor is incorporated in the hydraulic unit. When the brake pedal is depressed, the pressure sensor detects the brake pressure applied from the master cylinder, converts this pressure into the voltage signal, and outputs it.

DIAGNOSIS CODE SET CONDITIONS

When the pressure sensor output signal is not within the standard value range, ASC-ECU outputs this diagnosis code.

PROBABLE CAUSES

Incorrect adjustment of brake pedal height
Master cylinder malfunction
Brake booster malfunction
ASC-ECU malfunction

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics

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. C121D set?

	Go to Step 3.

	This diagnosis is complete.

STEP 3. Brake pedal check

Refer to GROUP 35A - On-vehicle Service

Q. Is the check result normal?

	Go to Step 4.

	Go to GROUP 35A - On-vehicle Service .

STEP 4. Check the installation condition of the stop lamp switch.

Refer to GROUP 35A - On-vehicle Service

Q. Is the check result normal?

	Go to Step 5.

	Install the stop lamp switch correctly, and then go to Step 7.

STEP 5. Brake booster check

Refer to GROUP 35A - On-vehicle Service

Q. Is the check result normal?

	Go to Step 6.

	After replacing the brake booster, go to Step 7.

STEP 6. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.C121D set?

	Replace the ASC-ECU (Refer to ).

	The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 7. Check whether the diagnosis code is reset.

Q. Is diagnosis code No.C121D set?

	Return to Step 1.

	This diagnosis is complete.