DTC C120F: Open in Master Reservoir Level Switch Circuit [10/2018 - ]: Procedure

1. Check that the brake fluid level is sufficient.

   HINT: 

   If the fluid level is low, check for fluid leaks, and repair as necessary.

   1. Check for brake fluid leaks (connection between the brake booster pump assembly, brake actuator assembly, brake booster with master cylinder assembly and wheel cylinders).

      HINT: 

      If no leaks exist, add and adjust fluid using the Techstream.

      Refer to ON-VEHICLE INSPECTION [10/2018 - ]

2. Check that there are no leaks from the connections between the brake booster pump assembly, brake actuator assembly and brake booster with master cylinder assembly.

   HINT: 

   As a visual check is very difficult, perform the check with the following procedure.

   1. Bleed the air from the brake system.

      Refer to BLEEDING [10/2018 - ]

   2. Turn the power switch off.
   3. Disconnect the A41 brake pedal stroke sensor assembly connector.
   4. Select the Data List on the Techstream.

      Refer to DATA LIST / ACTIVE TEST [10/2018 - ]

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display	Measurement Item	Range	Normal Condition	Diagnostic Note
      MT Voltage Value	MT voltage value	Min.: 0.00 V, Max.: 20.00 V	Pump motor off: 0.00 V Pump motor on: 12.00 V	-
      Accumulator Pressure	Accumulator pressure output value	Min.: 0.00 MPa, Max.: 24.48 MPa	15.00 to 21.00 MPa (Pressure stable and pump motor stopped)	When brake fluid is stored in the accumulator: Accumulator pressure changes in accordance with volume of fluid stored in the accumulator

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display
      MT Voltage Value
      Accumulator Pressure

   5. Depress the brake pedal several times to operate the pump motor, then wait until it stops.
   6. After the pump motor stops, wait for 30 seconds, then check the drop in the accumulator pressure sensor output value and the state of the pump motor.

   Result

   Result	Proceed to
   The drop in the accumulator pressure sensor output value is less than 2.50 MPa 30 seconds after the pump motor stops, and the pump motor does not operate within 30 seconds after the pump motor stops.	A
   The drop in the accumulator pressure sensor output value is 2.50 MPa or more 30 seconds after the pump motor stops, or the pump motor operates within 30 seconds after the pump motor stops.	B

Result: 

B 

CHECK AND REPAIR BRAKE FLUID LEAKS OR ADD FLUID 

Result: 

A 

See step  2

1. Turn the power switch off.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *a	Component without harness connected (Brake Fluid Level Warning Switch (Brake Booster with Master Cylinder Assembly))

2. Reconnect the A41 brake pedal stroke sensor assembly connector.
3. Remove the brake master cylinder reservoir filler cap assembly.
4. Make sure that there is no looseness at the locking part and the connecting part of the connector.

   OK

   The connector is securely connected.

5. Disconnect the A39 brake fluid level warning switch (brake booster with master cylinder assembly) connector.
6. Check both the connector case and the terminals for deformation and corrosion.

   OK

   No deformation or corrosion.

7. Measure the resistance according to the value(s) in the table below.

   HINT: 

   A float is located inside the brake master cylinder reservoir assembly. Its position changes according to the level of brake fluid.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   2 (LBL) - 1 (GND)	Brake fluid level warning switch (brake booster with master cylinder assembly) off (float up)	1.84 to 2.16 kΩ
   2 (LBL) - 1 (GND)	Brake fluid level warning switch (brake booster with master cylinder assembly) on (float down)	Below 1 Ω (Brake fluid level is low)

8. If there are no problems after completing the preceding inspection, adjust the brake fluid to the MAX level with the power switch on (IG).

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY. Refer to  REMOVAL [10/2018 - 07/2022]  , or refer to  REMOVAL [07/2022 - ] 

Result: 

OK 

See step  3

1. Turn the power switch off.
2. Make sure that there is no looseness at the locking part and the connecting part of the connector.

   OK

   The connector is securely connected.

3. Disconnect the A37 skid control ECU (brake booster with master cylinder assembly) connector.
4. Check both the connector case and the terminals for deformation and corrosion.

   OK

   No deformation or corrosion.

5. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   A37-16 (LBL) - A39-2 (LBL)	Always	Below 1 Ω
   A37-16 (LBL) or A39-2 (LBL) - Body ground	Always	10 kΩ or higher
   A39-1 (GND) - Body ground	Always	Below 1 Ω

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR 

Result: 

OK 

See step  4

1. Reconnect the A37 skid control ECU (brake booster with master cylinder assembly) connector.
2. Reconnect the A39 brake fluid level warning switch (brake booster with master cylinder assembly) connector.
3. Disconnect the A41 brake pedal stroke sensor assembly connector.
4. Perform a road test according to Freeze Frame Data or customer problem analysis. While driving, check for abnormal brake pedal vibration caused by brake discs that are worn or have excess runout.

   OK

   Brake pedal does not vibrate during braking.

   HINT: 

   • An unevenly worn disc may vibrate the caliper pistons and cause fluctuations in brake line pressure, triggering a malfunction detection condition.
   • The brake pedal does not kick back due to caliper piston vibration during electronically controlled brake system control.
   • If the brake pedal stroke sensor assembly connector is disconnected, the fail-safe function will prohibit electronically controlled brake system control.
   • The Active Test does not prohibit electronically controlled brake system control when the vehicle is being driven, so disconnect the brake pedal stroke sensor assembly connector before continuing with inspection.
   • Uneven disc wear can be checked by measuring the disc thickness variation.

     for Front Brake: Refer to INSPECTION [10/2018 - ]

     for Rear Brake: Refer to INSPECTION [10/2018 - ]

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPLACE BRAKE DISC 

Result: 

OK 

See step  5

1. Turn the power switch off.
2. Reconnect the A41 brake pedal stroke sensor assembly connector.
3. Clear the DTCs.

   Refer to DTC CHECK / CLEAR [10/2018 - ]

   Chassis > ABS/VSC/TRAC > Clear DTCs 

4. Turn the power switch off.
5. Turn the power switch on (READY).
6. Perform a road test.
7. Check if the same DTC is output.

   Refer to DTC CHECK / CLEAR [10/2018 - ]

   Chassis > ABS/VSC/TRAC > Trouble Codes 

   Result

   Result	Proceed to
   DTC C120F is not output.	A
   DTC C120F is output.	B

Result: 

A 

USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [10/2018 - ] 

Result: 

B 

REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY. Refer to  REMOVAL [10/2018 - 07/2022]  , or refer to  REMOVAL [07/2022 - ]