C121D
DTC C121D: Abnormality in brake fluid pressure sensor circuit
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 CAN Bus Line Diagnostics Flow ).
- 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 Testing and Inspection , Testing and Inspection and Testing and Inspection ).
- Whenever ECU is replaced, ensure that the CAN bus lines are normal.
CIRCUIT OPERATION
The brake fluid pressure 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.
DTC SET CONDITIONS
When the pressure sensor output signal is not within the standard value range, ASC-ECU sets this diagnostic trouble code.
PROBABLE CAUSES
- Incorrect brake pedal height
- Incorrect adjustment of the stoplight switch
- Master cylinder malfunction
- Brake booster malfunction
- ASC-ECU malfunction
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 C121D set?
YES Go to Step 3.
NO The procedure is complete.
STEP 3. Brake pedal check
Brake Pedal Inspection.
Q. Is the check result normal?
YES Go to Step 4.
NO Go to On-vehicle Service/Brake Pedal Inspection Brake Pedal Inspection.
STEP 4. Check the installation condition of the stoplight switch.
Brake Pedal Inspection.
Q. Is the check result normal?
YES Go to Step 5.
NO Install the stop light switch correctly Brake Pedal Inspection), and then go to Step 7 .
STEP 5. Brake booster check
Testing and Inspection.
Q. Is the check result normal?
YES Go to Step 6.
NO After replacing the brake booster Service and Repair), go to Step 7.
STEP 6. Check whether the diagnostic trouble code is reset.
Erase the DTC.
Q. Is DTC C121D set?
YES Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Service and Repair).
NO The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 7. Check whether the diagnostic trouble code is reset.
Erase the DTC.
Q. Is DTC C121D set?
YES Return to Step 1.
NO The procedure is complete.