Lexus NX: Accumulator Low Pressure (C1256)
DESCRIPTION
The accumulator pressure sensor is built into the brake actuator (brake booster with master cylinder assembly) and detects the accumulator pressure.
The skid control ECU (brake booster with master cylinder assembly) turns on the brake warning light / red (malfunction) and brake warning light / yellow (minor malfunction), and sounds the meter buzzer if it senses a decrease in the accumulator pressure.
DTC C1256 may be stored if the accumulator pressure drops due to frequent braking (this is not a malfunction).
| DTC No. | Detection Item | INF Code | DTC Detection Condition | Trouble Area | Note |
|---|---|---|---|---|---|
| C1256 | Accumulator Low Pressure | 341 | Significant drop in accumulator pressure continues. (DTCs will be stored and the buzzer will operate when either condition is met.) |
| - |
WIRING DIAGRAM
Refer to DTCs C1252 and C1253.
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CAUTION / NOTICE / HINT
NOTICE:
-
When replacing the brake actuator (brake booster with master cylinder assembly), perform initialization and calibration of the linear solenoid valve.
Click here
- Inspect the fuses for circuits related to this system before performing the following procedure.
HINT:
When C1202, C1241, C1252, C1253 and/or C1391 are output together with C1256, inspect and repair the trouble areas indicated by C1202, C1241, C1252, C1253 and/or C1391 first.
for C1202: Click here
for C1241: Click here
for C1252 and C1253: Click here
for C1391: Click here
PROCEDURE
| 1. | BRAKE PROBLEM CHECK |
(a) Ask the customer if frequent braking was performed while the brake warning light / yellow (minor malfunction) was on.
| Result | Proceed to |
|---|---|
| Frequent braking was not performed. | A |
| Frequent braking was performed. | B |
HINT:
This DTC may be stored even if the accumulator pressure drops only temporarily due to frequent braking.
| B | .gif) | END |
|
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| 2. | INSPECT BRAKE BOOSTER PUMP ASSEMBLY |
| (a) Make sure that there is no looseness at the locking part and the connecting part of the connectors. |
|
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(b) Disconnect the A51 and A52 brake booster pump assembly connectors.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| A51-1 (BM1) - A51-2 (GND1) | Always | Below 10 Ω |
| A52-2 (BM2) - A52-1 (GND2) | Always | Below 10 Ω |
| A51-1 (BM1) - A52-2 (BM2) | Always | Below 1 Ω |
| A51-2 (GND1) - A52-1 (GND2) | Always | Below 1 Ω |
| NG | | REPLACE BRAKE BOOSTER PUMP ASSEMBLY |
|
| 3. | READ VALUE USING TECHSTREAM (ACCUMULATOR PRESSURE SENSOR) |
(a) Reconnect the A51 and A52 brake booster pump assembly connectors.
(b) Connect the Techstream to the DLC3.
(c) Turn the power switch on (IG).
(d) Select the Data List on the Techstream.
Click here
| Tester Display | Measurement Item | Range | Normal Condition | Diagnostic Note |
|---|---|---|---|---|
| Accumulator Sensor | Accumulator pressure sensor | Min.: 0.00 V, Max.: 5.00 V | Specified value: 2.90 to 4.20 V | When brake fluid is stored in the accumulator: Accumulator pressure changes in accordance with volume of fluid stored in the accumulator |
| Tester Display |
|---|
| Accumulator Sensor |
(e) Depress the brake pedal 4 or 5 times to operate the pump motor.
(f) Wait for 30 seconds without depressing the brake pedal.
(g) Check that the accumulator pressure sensor output value change is within the specified range.
OK:
Accumulator pressure sensor output value change is less than 0.55 V.
| OK | | USE SIMULATION METHOD TO CHECK |
|
| 4. | PERFORM ACTIVE TEST USING TECHSTREAM (SOLENOID VALVE) |
(a) Select the Active Test on the Techstream.
Click here
| Tester Display | Measurement Item | Control Range | Diagnostic Note |
|---|---|---|---|
| ECB Solenoid (SMC/SRC/SCC) | Switching solenoid valve (SMC/SRC/SCC) | Solenoid ON/OFF |
|
| Tester Display |
|---|
| ECB Solenoid (SMC/SRC/SCC) |
HINT:
The Active Test can be performed when the following conditions are met.
- ABS main relay is on.
- Shift lever is in P.
- Parking brake is applied.
- Vehicle speed is 0 km/h (0 mph).
(b) Perform the Active Test of the solenoid using the Techstream.
(c) Select the Data List on the Techstream.
Click here
| Tester Display | Measurement Item | Range | Normal Condition | Diagnostic Note |
|---|---|---|---|---|
| Wheel Cylinder Pressure Sensor | Wheel cylinder pressure sensor | Min.: 0.00 V, Max.: 5.00 V | Brake pedal released: 0.10 to 0.90 V | Reading increases when brake pedal is depressed |
| Tester Display |
|---|
| Wheel Cylinder Pressure Sensor |
(d) Check that the output value of the wheel cylinder pressure sensor does not increase.
OK:
The output value of the wheel cylinder pressure sensor does not increase.
HINT:
If the output value increases, there may be brake fluid leaks in the brake actuator.
| OK | | REPLACE BRAKE BOOSTER PUMP ASSEMBLY |
| NG | | REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY |
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DISASSEMBLY CAUTION / NOTICE / HINT NOTICE: Do not allow any dirt (fingerprints, grease, etc.) to adhere to the meter glass. If the glass is dirty, wipe it clean with a soft cloth. PROCEDURE 1. REMOVE COMBINATION METER GLASS (a) Using a screwdriver, detach the 8 claws and remove the combination m
