BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: ELECTRONICALLY CONTROLLED BRAKE SYSTEM (for HV Model): C137BA2; Brake System Control Module "A" System Voltage System Voltage Low; 2023 - 2026 MY Corolla Corolla HV [09/2022

Last Modified: 08-22-2025	6.11:8.1.0	Doc ID: RM0000003TPCML5
Model Year Start: 2023	Model: Corolla	Prod Date Range: [09/2022 - ]
Title: BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: ELECTRONICALLY CONTROLLED BRAKE SYSTEM (for HV Model): C137BA2; Brake System Control Module "A" System Voltage System Voltage Low; 2023 - 2026 MY Corolla Corolla HV [09/2022 - ]

DTC

C137BA2

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

DESCRIPTION

Refer to DTC C117A49.

Click here

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	MIL	DTC Output from	Note
C137BA2	Brake System Control Module "A" System Voltage System Voltage Low	Any of the following is detected: 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.	Wire harness or connector Skid control ECU (brake actuator assembly)	Does not come on	Brake/EPB	Output ECU: Skid control ECU (brake actuator assembly)

WIRING DIAGRAM

Refer to DTC C117A49.

Click here

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 auxiliary 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/EPB

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 auxiliary 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 auxiliary battery voltage

HINT:

This is the voltage detected at terminal +BM (which supplies power to the ABS motor) 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 AUXILIARY BATTERY

REPLACE BRAKE ACTUATOR ASSEMBLY

2.	READ VALUE USING GTS (+BS VOLTAGE)

(a) Turn the ignition switch to ON (READY).

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

Chassis > Brake/EPB > 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 auxiliary 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/EPB > 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 connector.

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

Standard Resistance:

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

REPLACE BRAKE ACTUATOR ASSEMBLY

REPAIR OR REPLACE HARNESS OR CONNECTOR