Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Brake System Control Module "A" System Voltage System Voltage Low (C137BA2)

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Brake / Brake Control / Dynamic Control Systems / Vehicle Stability Control System / 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:

  • When the +BS terminal voltage is below 9.5 V, the power source voltage for all speed sensors is continuously low for 60 seconds or more.
  • After the +BS terminal voltage is below 9.5 V continuously for 3 seconds or more, the +BS terminal voltage is below 9.5 V continuously for 7 seconds or more at a vehicle speed exceeding 3 km/h (2 mph).
  • When the +BS terminal voltage is 9.5 V or higher and the vehicle speed exceeds 15 km/h (9 mph), the IG1 terminal voltage is 10 V or less continuously for 60 seconds or more.
  • When the +BS terminal voltage is below 9.5 V and the solenoid relay is ON, the relay contact is OFF continuously for 1.22 seconds or more.
  • When the +BS terminal voltage is below 9.5 V, motor fail-safe relay overcurrent continues for 1.05 seconds or more.
  • Battery
  • Charging system
  • Wire harness and connector
  • Skid control ECU (brake actuator assembly)
DTC Detection Conditions: C137BA2
 

Vehicle Condition

Pattern 1

Pattern 2

Pattern 3

Pattern 4

Pattern 5

Diagnosis Condition

When the +BS terminal voltage is below 9.5 V

○

-

-

-

○

The +BS terminal voltage is below 9.5 V for 3 seconds or more and the vehicle is driven at 3 km/h (2 mph) or more

-

○

-

-

-

When the +BS terminal voltage is 9.5 V or higher and the vehicle speed exceeds 15 km/h (9 mph)

-

-

○

-

-

When the +BS terminal voltage is below 9.5 V and the solenoid relay is ON

-

-

-

○

-

Malfunction Status

The power source voltage for all speed sensors is continuously low

○

-

-

-

-

The +BS terminal voltage is below 9.5 V continuously

-

○

-

-

-

The IG1 terminal voltage is 10 V or less continuously

-

-

○

-

-

The relay contact is OFF continuously

-

-

-

○

-

Motor fail-safe relay overcurrent continues

-

-

-

-

○

Detection Time

60 seconds or more

7 seconds or more

60 seconds or more

1.22 seconds or more

1.05 seconds or more

Number of Trips

1 trip

1 trip

1 trip

1 trip

1 trip

HINT:

DTC will be output when conditions for any 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 "Calibration".

    Click here

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 OR BATTERY

OK

2.

CHECK HARNESS AND CONNECTOR (+BS 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.

*a

Front view of wire harness connector

(to Skid Control ECU (Brake Actuator Assembly))

(b) Disconnect the A41 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

A41-14 (+BS) - Body ground

Always

11 to 14 V
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (+BS CIRCUIT)
OK

3.

CHECK HARNESS AND CONNECTOR (IG1 TERMINAL)

(a) Turn the engine switch on (IG).

*a

Front view of wire harness connector

(to Skid Control ECU (Brake Actuator Assembly))

(b) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection

Condition

Specified Condition

A41-45 (IG1) - Body ground

Engine switch on (IG)

11 to 14 V
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

4.

CHECK HARNESS AND CONNECTOR (GND1 TERMINAL)

(a) Turn the engine switch off.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

A41-1 (GND1) - Body ground

1 minute or more after disconnecting the cable from the negative (-) battery terminal

Below 1 Ω
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

5.

CLEAR DTC

(a) Reconnect the A41 skid control ECU (brake actuator assembly) connector.

(b) Connect the Techstream to the DLC3.

(c) Turn the engine switch on (IG).

(d) Operate the Techstream to clear the codes. Enter the following menus: Chassis / Brake/EPB / Trouble Codes.

Chassis > Brake/EPB > Clear DTCs

(e) Press the DTC clear button.

(f) Turn the engine switch off.

NEXT

6.

RECONFIRM DTC

(a) Start the engine.

(b) Perform a road test.

(c) Read the DTCs following the prompts on the Techstream. Enter the following menus: Chassis / Brake/EPB / Trouble Codes.

Chassis > Brake/EPB > Trouble Codes

(d) Check if the same DTC is output.

Result

Proceed to

DTC C137BA2 is not output.

A

DTC C137BA2 is output.

B
A

USE SIMULATION METHOD TO CHECK

B

REPLACE BRAKE ACTUATOR ASSEMBLY

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