C121E
DTC C121E: Abnormality in brake fluid pressure sensor output signal
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 ).
- 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 Testing and Inspection , Testing and Inspection and Testing and Inspection ).
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.
DTC SET CONDITIONS
This diagnostic trouble 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 stoplight switch
- Stoplight switch malfunction
- Brake drag
- ASC-ECU malfunction
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus line.
Use scan tool MB991958 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. Diagnostic trouble code recheck after resetting CAN bus lines
Q. Is DTC C121E 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 whether the other system diagnostic trouble code is set.
Rear Combination Light.
Q. Is any DTC set?
YES Repair or replace the rear combination light or rear combination light circuit.
NO Go to Step 5.
STEP 5. Check for stoplight switch installation
Brake Pedal Inspection.
Q. Is the check result normal?
YES Go to Step 6.
NO Install the stop light switch correctly Brake Pedal Inspection), and then go to Step 10 .
STEP 6. Stoplight switch continuity check
(1)Remove the stoplight switch Service and Repair).
(2)Connect the circuit tester (ohms
range) to the stop light switch connector terminals No.1 and No.2.
(3)When no continuity is detected with the plunger pressed from the edge of the outer case by the dimension shown in the figure and when continuity is detected with the plunger released, the stop light switch is in good condition.
Q. Is the check result normal?
YES Go to Step 7.
NO Replace the stop light switch Service and Repair), and then go to Step 10.
STEP 7. Brake drag check
Check the brake system for drag Brake Drag Force Check).
Q. Is the check result normal?
YES Go to Step 8.
NO Repair the brake drag, and then go to Step 10.
STEP 8. Brake booster check
Testing and Inspection.
Q. Is the check result normal?
YES Go to Step 9.
NO Replace the brake booster Service and Repair), and then go to Step 10.
STEP 9. Check whether the diagnostic trouble code is reset.
Erase the DTC.
Q. Is DTC C121E set?
YES Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Service and Repair).
Then go to Step 10.
NO The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 10. Check whether the diagnostic trouble code is reset.
Erase the DTC.
Q. Is DTC C121E set?
YES Return to Step 1.
NO The procedure is complete.