C121E
DTC C121E Abnormality in brake fluid pressure sensor output signalCAUTION
^ 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.
^ 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.
OPERATION
The hydraulic 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
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 (Refer to CAN Bus Diagnostic table CAN Bus Diagnostics Table). 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
Refer to On-vehicle Service Brake Pedal Check and Adjustment.
Q: Is the check result normal?
YES: Go to Step 4.
NO: Adjust the brake pedal height. (Refer to On-vehicle Service Brake Pedal Check and Adjustment). Then go to Step 9.
STEP 4. Check for stoplight switch installation
Refer to On-vehicle Service Brake Pedal Check and Adjustment.
Q: Is the check result normal?
YES: Go to Step 5.
NO: Install the stoplight switch correctly (Refer to On-vehicle Service Brake Pedal Check and Adjustment), and then go to Step 9.
STEP 5. stoplight switch continuity check
1) Remove the stoplight switch.
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, 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
Refer to On-vehicle Service Testing and Inspection.
Q: Is the check result normal?
YES: Go to Step 8.
NO: Replace the brake booster (Refer to Master Cylinder Assembly and Brake Booster [FWD], [AWD]), and then go to Step 9.
STEP 8. Check whether the DTC is reset.
Q: Is DTC C121E set?
YES: Replace the hydraulic unit (ASC-ECU). Then go to Step 9.
NO: The trouble can be an intermittent malfunction.
STEP 9. Check whether the DTC is reset.
Q: Is DTC C121 E set?
YES: Return to Step 1.
NO: The procedure is complete.