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DTC C121D Brake fluid pressure sensor circuit
 
 
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 (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.
 
 
 
DTC SET CONDITIONS
When the pressure sensor output signal is not within the standard value range, ASC-ECU outputs this DTC.
 
 
 
TROUBLESHOOTING HINTS
  • Incorrect brake pedal height
  • Incorrect adjustment of the stoplight switch
  • Master cylinder malfunction
  • Brake booster malfunction
  • ASC-ECU malfunction
 
 
 
 
DIAGNOSIS
STEP 1. Scan tool (M.U.T.-III) CAN bus diagnostics
(1)
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
Connect scan tool (M.U.T.-III). Refer to "How to connect the Scan Tool (M.U.T.-III) ."
(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
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. DTC recheck after resetting CAN bus lines
Is DTC No. C121D set?
Go to Step 3.
This diagnosis is complete.
 
STEP 3. Brake pedal check
Refer to GROUP 35A - On-vehicle Service/Brake Pedal Check .
Is the check result normal?
Go to Step 4.
Go to GROUP 35A - On-vehicle Service/Brake Pedal Check . Then go to Step 7.
 
STEP 4. Check the installation condition of the stoplight switch.
Refer to GROUP 35A - On-vehicle Service/Brake Pedal Check .
Is the check result normal?
Go to Step 5.
Install the stoplight switch correctly, and then go to Step 7.
 
STEP 5. Brake booster check
Refer to GROUP 35A - On-vehicle Service/Brake Booster Operation Check .
Is the check result normal?
Go to Step 6.
After replacing the brake booster, go to Step 7.
 
STEP 6. Check whether the DTC is set again.
Erase the DTC.
Is DTC No.C121D set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ). Then go to Step 7.
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions ).
 
STEP 7. Check whether the DTC is set again.
Erase the DTC.
Is DTC No.C121D set?
Return to Step 1.
This diagnosis is complete.