Lexus ES: Open in Master Reservoir Level Switch Circuit (C120F)
DESCRIPTION
| DTC No. | Detection Item | INF Code | DTC Detection Condition | Trouble Area | MIL | Note |
|---|---|---|---|---|---|---|
| C120F | Open in Master Reservoir Level Switch Circuit | 371 | The brake fluid level warning switch (brake booster with master cylinder assembly) circuit is open for 2 seconds or more. |
| Comes on |
|
MONITOR DESCRIPTION
When the voltage at terminal LBL of the skid control ECU (brake booster with master cylinder assembly) is a specific value or more (open circuit judgment range) for a certain amount of time, the skid control ECU (brake booster with master cylinder assembly) judges that there is an open in the fluid warning switch circuit and illuminates the MIL and stores this DTC.
MONITOR STRATEGY
| Related DTCs | C120F: Brake fluid level warning switch open circuit |
| Required Sensors/Components(Main) | Brake fluid level warning switch (brake booster with master cylinder assembly) |
| Required Sensors/Components(Related) | Skid control ECU (brake booster with master cylinder assembly) |
| Frequency of Operation | Continuous |
| Duration | 2 seconds |
| MIL Operation | Immediately |
| Sequence of Operation | None |
TYPICAL ENABLING CONDITIONS
| Monitor runs whenever the following DTCs are not stored | None |
| Serial communication with low side IC | Valid |
TYPICAL MALFUNCTION THRESHOLDS
| Brake fluid level warning switch voltage | Higher than 8.4 V |
COMPONENT OPERATING RANGE
| Both of the following conditions are met | - |
| Serial communication with low side IC | Valid |
| Brake fluid level warning switch voltage | 8.4 V or less |
CONFIRMATION DRIVING PATTERN
- Connect the Techstream to the DLC3.
- Turn the power switch on (IG).
- Turn the Techstream on.
- Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
- Turn the power switch off.
- Turn the power switch on (IG).
- Turn the Techstream on.
- Wait 2 seconds.
- Enter the following menus: Chassis / ABS/VSC/TRAC / Trouble Codes.
-
Read the DTCs.
HINT:
- If a DTC is output, the system is malfunctioning.
- If a DTC is not output, perform the following procedure.
-
If the DTCs are not output, perform a universal trip and check for permanent DTCs.
Click here
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HINT:
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTCs are output, the system is normal.
WIRING DIAGRAM
Refer to DTC C1202.
Click here
CAUTION / NOTICE / HINT
NOTICE:
After replacing the skid control ECU (brake booster with master cylinder assembly), perform linear solenoid valve offset learning, ABS holding solenoid valve learning, yaw rate and acceleration sensor zero point calibration and system information memorization after performing "Reset Memory".
Click here
PROCEDURE
| 1. | CHECK BRAKE FLUID LEVEL |
(a) 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.
Click here
(b) 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.
Click here
(2) Turn the power switch off.
(3) Disconnect the A44 brake pedal stroke sensor assembly connector.
(4) Select the Data List on the Techstream.
Click here
| 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 |
| 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 | 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 |
| B |  | CHECK AND REPAIR BRAKE FLUID LEAKS OR ADD FLUID |
|
| 2. | INSPECT BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY (BRAKE FLUID LEVEL WARNING SWITCH) |
| (a) Turn the power switch off. |
|
(b) Reconnect the A44 brake pedal stroke sensor assembly connector.
(c) Remove the brake master cylinder reservoir filler cap assembly.
(d) Make sure that there is no looseness at the locking part and the connecting part of the connector.
OK:
The connector is securely connected.
(e) Disconnect the A4 brake fluid level warning switch (brake booster with master cylinder assembly) connector.
(f) Check both the connector case and the terminals for deformation and corrosion.
OK:
No deformation or corrosion.
(g) Measure the resistance according to the value(s) in the table below.
HINT:
A float is located inside the brake master cylinder reservoir assembly (brake booster with master cylinder 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) |
(h) If there are no problems after completing the preceding inspection, adjust the brake fluid to the MAX level with the power switch on (IG).
| NG | | REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY |
|
| 3. | CHECK HARNESS AND CONNECTOR (BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY - BRAKE FLUID LEVEL WARNING SWITCH (BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY)) |
(a) Turn the power switch off.
(b) Make sure that there is no looseness at the locking part and the connecting part of the connector.
OK:
The connector is securely connected.
(c) Disconnect the A45 skid control ECU (brake booster with master cylinder assembly) connector.
(d) Check both the connector case and the terminals for deformation and corrosion.
OK:
No deformation or corrosion.
(e) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| A45-16 (LBL) - A4-2 (LBL) | Always | Below 1 Ω |
| A45-16 (LBL) or A4-2 (LBL) - Body ground | Always | 10 kΩ or higher |
| A4-1 (GND) - Body ground | Always | Below 1 Ω |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 4. | CHECK BRAKE DISC |
(a) Reconnect the A45 skid control ECU (brake booster with master cylinder assembly) connector.
(b) Reconnect the A4 brake fluid level warning switch (brake booster with master cylinder assembly) connector.
(c) Disconnect the A44 brake pedal stroke sensor assembly connector.
(d) 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: Click here
for Rear Brake: Click here
| NG | | REPLACE BRAKE DISC |
|
| 5. | RECONFIRM DTC |
(a) Turn the power switch off.
(b) Reconnect the A44 brake pedal stroke sensor assembly connector.
(c) Clear the DTCs.
Click here
(d) Turn the power switch off.
(e) Turn the power switch on (READY).
(f) Perform a road test.
(g) Check if the same DTC is output.
Click here
| Result | Proceed to |
|---|---|
| DTC C120F is not output. | A |
| DTC C120F is output. | B |
| A | | USE SIMULATION METHOD TO CHECK |
| B | | REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY |
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