Code No. C121E Brake fluid pressure sensor



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 Diagnostics Table ).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.

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


This diagnosis codes will be set under the cases below:

  • When the pressure sensor offset is not within the standard value range
  • When the estimated pressure sensor temperature is not normal

PROBABLE CAUSES



  • Incorrect adjustment of brake pedal height
  • Master cylinder malfunction
  • Brake booster malfunction
  • Incorrect installation position of stop lamp switch
  • Malfunction of the stop lamp switch
  • Brake drag
  • ASC-ECU malfunction

DIAGNOSTIC 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 Diagnostics Table ). On completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting CAN bus lines


Q. Is diagnosis code No. C121E set?

Go to Step 3.
This diagnosis is complete.

STEP 3. Brake pedal check


Refer to GROUP 35A - On-vehicle Service/Brake Pedal Check .

Q. Is the check result normal?

Go to Step 4.
Go to GROUP 35A - On-vehicle Service/Brake Pedal Check . Then go to Step 9.

STEP 4. Check for stop lamp switch installation


Refer to GROUP 35A - On-vehicle Service/Brake Pedal Check .

Q. Is the check result normal?

Go to Step 5.
Install the stop lamp switch correctly (Refer to GROUP 35A - On-vehicle Service/Brake Pedal Check ), and then go to Step 9.

STEP 5. Stop lamp switch continuity check


Refer to GROUP 35A - Brake Pedal .

Q. Is the check result normal?

Go to Step 6.
Replace the stop lamp switch (Refer to GROUP 35A -Brake Pedal ), and then go to Step 9.

STEP 6. Brake drag check


Check the brake system for drag.

Q. Is the check result normal?

Go to Step 7.
Repair the brake drag, and then go to Step 9.

STEP 7. Brake booster check


Refer to GROUP 35A - On-vehicle Service/Brake Booster Operation Check .

Q. Is the check result normal?

Go to Step 8.
Replace the brake booster <Refer to GROUP 35A - Master Cylinder Assembly and Brake Booster (LHD) or (RHD)>, and then go to Step 9.

STEP 8. Check whether the diagnosis code is reset.


Erase the diagnosis code.

Q. Is diagnosis code No. C121E set?

Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ). Then go to Step 9.
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions ).

STEP 9. Check whether the diagnosis code is reset.


Erase the diagnosis code.

Q. Is diagnosis code No.C121E set?

Return to Step 1.
This diagnosis is complete.