C121E
DTC C121E Abnormality in brake fluid pressure sensor output signal
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.
- 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 DTCs 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
- Malfunction of the stoplight switch
- Brake drag
- ASC-ECU malfunction
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A
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 C121E set?
YES Go to Step 3.
NO The procedure is complete.
STEP 3. Brake pedal check
Brake Pedal Check and Adjustment.
Q. Is the check result normal?
YES Go to Step 4.
NO Adjust the brake pedal height. Brake Pedal Check and Adjustment). Then go to Step 9.
STEP 4. Check for stoplight switch installation
Brake Pedal Check and Adjustment.
Q. Is the check result normal?
YES Go to Step 5.
NO Install the stoplight switch correctly Brake Pedal Check and Adjustment), and then go to Step 9.
STEP 5. stoplight switch continuity check
(1)Remove the stoplight switch Service and Repair).
(2)Connect the circuit tester (ohms range) to the stoplight switch connector terminals No.1 and 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 stoplight switch is in good condition.
Q. Is the check result normal?
YES Go to Step 6.
NO Replace the stoplight switch Service and Repair), and then go to Step 9.
STEP 6. Brake drag check
Check the brake system for drag.
Q. Is the check result normal?
YES Go to Step 7.
NO Repair the brake drag, and then go to Step 9.
STEP 7. Brake booster check
Testing and Inspection.
Q. Is the check result normal?
YES Go to Step 8.
NO Replace the brake booster Master Cylinder Assembly and Brake Booster Assembly Removal and Installation [Except Ralliart] [Except RALLIART], Master Cylinder Assembly and Brake Booster Assembly Removal and Installation [Ralliart] [RALLIART]), and then go to Step 9.
STEP 8. Check whether the DTC is reset.
Erase the DTC.
Q. Is DTC C121E set?
YES Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Active Stability Control System (ASC)).
Then go to Step 9.
NO The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 9. Check whether the DTC is reset.
Erase the DTC.
Q. Is DTC C121E set?
YES Return to Step 1.
NO The procedure is complete.