BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: ELECTRONICALLY CONTROLLED BRAKE SYSTEM (for Gasoline Model with Electric Parking Brake System): C137BA2; Brake System Control Module "A" System Voltage System Voltage Low; 2023 - 2026 MY Corolla Corolla Hatchback GR Corolla [11/2022

Last Modified: 08-22-2025	6.11:8.1.0	Doc ID: RM0000003TPCPUI
Model Year Start: 2023	Model: GR Corolla	Prod Date Range: [11/2022 - ]
Title: BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: ELECTRONICALLY CONTROLLED BRAKE SYSTEM (for Gasoline Model with Electric Parking Brake System): C137BA2; Brake System Control Module "A" System Voltage System Voltage Low; 2023 - 2026 MY Corolla Corolla Hatchback GR Corolla [11/2022 - ]

DTC

C137BA2

Brake System Control Module "A" System Voltage System Voltage Low

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	MIL	Note
C137BA2	Brake System Control Module "A" System Voltage System Voltage Low	The vehicle speed is 6 km/h (4 mph) or more and the +BS terminal voltage (soft low voltage) is less than 9.6 V for 1 second or more. The vehicle speed is 6 km/h (4 mph) or more and the +BS terminal voltage (hard low voltage) is less than 6.9 V for 1 second or more. 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 for 0.06 seconds or more. When the system has started, the +BS terminal voltage is less than 5 V for 0.5 seconds or more. The +BS terminal voltage is less than 2.6 V for 0.2 seconds or more.	Battery Charging system Wire harness or connector Internal power supply circuit of the skid control ECU (brake actuator assembly)	Does not come on	-

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Inspect the fuses for circuits related to this system before performing the following procedure.
Before performing troubleshooting, make sure to confirm that the battery voltage is normal.
Click here

PROCEDURE

1.	CHECK FREEZE FRAME DATA (+BS VOLTAGE AND +BM VOLTAGE)

(a) Select a DTC to display the Freeze Frame Data.

(b) Read the freeze frame data of DTC C137BA2.

Chassis > Brake

Tester Display

Measurement Item

Range

Normal Condition

Diagnostic Note

+BS Voltage

+BS voltage value (value detected by ECU)

Min.: 0.0 V, Max.: 25.5 V

Ignition switch ON: 11.0 to 14.0 V

Changes in proportion to battery voltage

HINT:

This is the voltage detected at terminal +BS (which supplies power to each solenoid) of the skid control ECU (brake actuator assembly)

+BM Voltage

+BM voltage value (value detected by ECU)

Min.: 0.0 V, Max.: 25.5 V

Ignition switch ON: 11.0 to 14.0 V

Changes in proportion to battery voltage

HINT:

This is the voltage detected at terminal +BM (which supplies power to each solenoid) of the skid control ECU (brake actuator assembly)

Chassis > Brake/EPB > DTC(C137BA2) > Freeze Frame Data

Tester Display
+BS Voltage
+BM Voltage

Result	Proceed to
+BS Voltage and +BM Voltage are less than 9.6 V.	A
Only +BS Voltage is less than 9.6 V.	B
Only +BM Voltage is less than 9.6 V, or both +BS Voltage and +BM Voltage are 9.6 V or more.	C

CHECK OR REPLACE CHARGING SYSTEM COMPONENT OR BATTERY

REPLACE BRAKE ACTUATOR ASSEMBLY

2.	READ VALUE USING GTS (+BS VOLTAGE)

(a) Start the engine.

(b) Follow the instructions on the screen to display the Data List, and perform the inspection.

Chassis > Brake > Data List

Tester Display

Measurement Item

Range

Normal Condition

Diagnostic Note

+BS Voltage

+BS voltage value (value detected by ECU)

Min.: 0.0 V, Max.: 25.5 V

Ignition switch ON: 11.0 to 14.0 V

Changes in proportion to battery voltage

HINT:

This is the voltage detected at terminal +BS (which supplies power to each solenoid) of the skid control ECU (brake actuator assembly)

Chassis > Brake > Data List

Tester Display
+BS Voltage

Result	Proceed to
The value of +BS Voltage is 9.6 V or more.	A
The value of +BS Voltage is less than 9.6 V.	B

USE SIMULATION METHOD TO CHECK

3.	CHECK HARNESS AND CONNECTOR (+BS 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.

*a	Front view of wire harness connector (to Skid Control ECU (Brake Actuator Assembly))

(b) Disconnect the A51 skid control ECU (brake actuator assembly) connector.

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
A51-30 (+BS) - Body ground	Always	9.6 V or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

4.	CHECK HARNESS AND CONNECTOR (GND1 TERMINAL)

(a) Make sure that there is no looseness at the locking part and the connecting part of the connectors.

OK:

The connector is securely connected.

(b) Disconnect the A51 skid control ECU (brake actuator assembly) connector.

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
A51-46 (GND1) - Body ground	1 minute or more after disconnecting the cable from the negative (-) battery terminal	Below 1 Ω

REPLACE BRAKE ACTUATOR ASSEMBLY

REPAIR OR REPLACE HARNESS OR CONNECTOR