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DTC C121E Brake fluid pressure sensor
 
 
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
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
 
 
 
TROUBLESHOOTING HINTS
  • 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
STEP 1. Scan tool (M.U.T.-IIISE) CAN bus diagnosis.
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect the Scan Tool (M.U.T.-IIISE) ."
(2) Turn on the power supply mode of the electric motor switch.
(3) Diagnose the CAN bus line.
(4) Turn off the power supply mode of the electric motor switch.
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. C121E 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 9.
 
STEP 4. Check for stoplight switch installation.
Refer to GROUP 35A - On-vehicle Service/Brake Pedal Check .
Is the check result normal?
Go to Step 5.
Install the stoplight switch correctly (Refer to GROUP 35A - On-vehicle Service/Brake Pedal Check ), and then go to Step 9.
 
STEP 5. Stoplight switch continuity check.
Refer to GROUP 35A - Brake Pedal .
Is the check result normal?
Go to Step 6.
Replace the stoplight switch, and then go to Step 9.
 
STEP 6. Brake drag check.
Check the brake system for drag.
Is the check result normal?
Go to Step 7.
Repair the brake drag (Refer to GROUP 35A - Symptom Procedures 4 "Brake drag "), and then go to Step 9.
 
STEP 7. Brake booster check.
Refer to GROUP 35A - On-vehicle Service/Brake Booster Operation Check .
Is the check result normal?
Go to Step 8.
Replace the brake booster (Refer to GROUP 35A - Master Cylinder Assembly and Brake Booster ), and then go to Step 9.
 
STEP 8. Check whether the DTC is set again.
Erase the DTC.
Is DTC No. C121E set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ). Then go to Step 9.
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions ).
 
STEP 9. Check whether the DTC is set again.
Erase the DTC.
Is DTC No.C121E set?
Return to Step 1.
This diagnosis is complete.