Lexus ES: Brake System Control Module "A" System Voltage System Voltage Low (C137BA2)
DESCRIPTION
If a malfunction is detected in the power supply circuit, the skid control ECU (brake actuator assembly) stores this DTC and the fail-safe function prohibits ABS operation.
This DTC is stored when the +BS terminal voltage meets one of the DTC detection conditions due to a malfunction in the power supply or charging circuit such as the battery or alternator circuit, etc.
The DTC is cleared when the +BS terminal voltage returns to normal.
| DTC No. | Detection Item | DTC Detection Condition | Trouble Area |
|---|---|---|---|
| C137BA2 | Brake System Control Module "A" System Voltage System Voltage Low | Any of the following is detected:
|
|
*: The skid control ECU (brake actuator assembly) monitors the resistance of the power source line at the +BS terminal. A malfunction is detected when an abnormality occurs in the +BS terminal wire harness or its connection and the skid control ECU (brake actuator assembly) determines that the wiring resistance at the +BS terminal exceeds the standard resistance.
DTC Detection Conditions: C137BA2| Vehicle Condition | |||||||
|---|---|---|---|---|---|---|---|
| Pattern 1 | Pattern 2 | Pattern 3 | Pattern 4 | Pattern 5 | Pattern 6 | ||
| Diagnosis Condition | The vehicle speed is 6 km/h (4 mph) or more. | ○ | ○ | - | - | - | - |
| The vehicle speed is 15 km/h (9 mph) or more and the +BS terminal voltage is 9.6 V or more. | - | - | - | ○ | - | - | |
| The system has started. | - | - | - | - | ○ | - | |
| Malfunction Status | The +BS terminal voltage (soft low voltage) is less than 9.6 V. | ○ | - | - | - | - | - |
| The +BS terminal voltage (hard low voltage) is less than 6.9 V. | - | ○ | - | - | - | - | |
| The +BS terminal voltage is less than 6.7 V and the skid control ECU (brake actuator assembly) judges that power supply voltage is abnormal. | - | - | ○ | - | - | - | |
| The skid control ECU (brake actuator assembly) turns on more than one valve at the same time within a short period of time and the valve relay supply voltage drop exceeds the threshold.* | - | - | - | ○ | - | - | |
| The +BS terminal voltage is less than 5 V. | - | - | - | - | ○ | - | |
| The +BS terminal voltage is less than 2.6 V. | - | - | - | - | - | ○ | |
| Detection Time | 1 second or more. | 1 second or more. | 0.06 seconds or more. | - | 0.5 seconds or more. | 0.2 seconds or more. | |
| Number of Trips | 1 trip | 1 trip | 1 trip | 1 trip | 1 trip | 1 trip | |
*: The skid control ECU (brake actuator assembly) monitors the resistance of the power source line at the +BS terminal. A malfunction is detected when an abnormality occurs in the +BS terminal wire harness or its connection and the skid control ECU (brake actuator assembly) determines that the wiring resistance at the +BS terminal exceeds the standard resistance.
HINT:
DTC will be output when conditions for either of the patterns in the table above are met.
WIRING DIAGRAM
CAUTION / NOTICE / HINT
NOTICE:
- Inspect the fuses for circuits related to this system before performing the following procedure.
-
After replacing the skid control ECU (brake actuator assembly), perform acceleration sensor zero point calibration and store system information memorization.
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PROCEDURE
| 1. | CHECK BATTERY |
(a) Check the battery voltage.
Standard Voltage:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| Positive (+) terminal - Negative (-) terminal | Always | 11 to 14 V |
| NG |  | CHECK OR REPLACE CHARGING SYSTEM COMPONENT OR BATTERY |
|
| 2. | CHECK HARNESS AND CONNECTOR (POWER SOURCE TERMINAL) |
| (a) Make sure that there is no looseness at the locking part and the connecting part of the connector. OK: The connector is securely connected. |
|
(b) Disconnect the A40 skid control ECU (brake actuator assembly) connector.
(c) Check both the connector case and the terminals for deformation and corrosion.
OK:
No deformation or corrosion.
(d) Measure the voltage according to the value(s) in the table below.
Standard Voltage:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| A40-30 (+BS) - Body ground | Always | 11 to 14 V |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
| 3. | CHECK HARNESS AND CONNECTOR (POWER SOURCE TERMINAL) |
| (a) Make sure that there is no looseness at the locking part and the connecting part of the connector. OK: The connector is securely connected. |
|
(b) Disconnect the A40 skid control ECU (brake actuator assembly) connector.
(c) Check both the connector case and the terminals for deformation and corrosion.
OK:
No deformation or corrosion.
(d) Measure the voltage according to the value(s) in the table below.
Standard Voltage:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| A40-1 (+BM) - Body ground | Always | 11 to 14 V |
| OK | | REPLACE BRAKE ACTUATOR ASSEMBLY |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
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