Toyota Tundra Service Manual: Brake Warning Light Remains ON

DESCRIPTION

The skid control ECU (brake actuator assembly) is connected to the combination meter assembly via CAN communication.

If any of the following is detected, the brake warning light remains on:

  • The skid control ECU (brake actuator assembly) connector is disconnected from the skid control ECU (brake actuator assembly).
  • The brake fluid level is insufficient.
  • EBD operation is not possible.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • When replacing the skid control ECU (brake actuator assembly), perform system variant learning and acceleration sensor zero point calibration.

    Click here

  • Inspect the fuses for circuits related to this system before performing the following procedure.
  • Before performing this procedure, depress the brake pedal and confirm that the stop lights illuminate.

PROCEDURE

1.

CHECK CAN COMMUNICATION SYSTEM

(a) Check if CAN communication system DTCs are output.

Click here

Result

Proceed to

DTCs are not output

A

DTCs are output

B

B

INSPECT CAN COMMUNICATION SYSTEM

A

2.

CHECK IF BRAKE ACTUATOR ASSEMBLY CONNECTOR IS SECURELY CONNECTED

(a) Check if the skid control ECU (brake actuator assembly) connector is securely connected.

OK:

The connector is securely connected.

NG

CONNECT CONNECTOR TO BRAKE ACTUATOR ASSEMBLY CORRECTLY

OK

3.

CHECK BATTERY

(a) Check the battery voltage.

Standard Voltage:

Tester Connection

Condition

Specified Condition

Positive (+) terminal - Negative (-) terminal

Ignition switch off

11 to 14 V

NG

CHECK OR REPLACE CHARGING SYSTEM COMPONENT OR BATTERY

OK

4.

CHECK HARNESS AND CONNECTOR (POWER SOURCE TERMINAL)

(a) Turn the ignition switch off.

*a

Front view of wire harness connector

(to Skid Control ECU (Brake Actuator Assembly))

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

OK:

The connector is securely connected.

(c) Disconnect the A57 skid control ECU (brake actuator assembly) connector.

(d) Check both the connector case and the terminals for deformation and corrosion.

OK:

No deformation or corrosion.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

A57-25 (+BS) - Body ground

Always

11 to 14 V

A57-6 (IG1) - Body ground

Ignition switch ON

11 to 14 V

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (POWER SOURCE CIRCUIT)

OK

5.

CHECK HARNESS AND CONNECTOR (GND1 TERMINAL)

(a) Turn the ignition switch off.

*a

Front view of wire harness connector

(to Skid Control ECU (Brake Actuator Assembly))

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

A57-38 (GND1) - Body ground

Always

Below 1 Ω

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (GND1 CIRCUIT)

OK

6.

INSPECT BRAKE MASTER CYLINDER RESERVOIR SUB-ASSEMBLY

(a) Turn the ignition switch off.

*a

Component without harness connected

(Brake Fluid Level Warning Switch (Brake Master Cylinder Reservoir Sub-assembly))

(b) Reconnect the A57 skid control ECU (brake actuator assembly) connector.

(c) Remove the reservoir filler cap and strainer.

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

OK:

The connector is securely connected.

(e) Disconnect the A3 brake fluid level warning switch (brake master cylinder reservoir sub-assembly) connector.

(f) Check both the connector case and the terminals for deformation and corrosion.

OK:

No deformation or corrosion.

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

HINT:

A float is located inside the reservoir. Its position changes according to the brake fluid level.

Standard Resistance:

Tester Connection

Condition

Specified Condition

1 (+) - 2 (E)

Switch off (float up)

10 kΩ or higher

1 (+) - 2 (E)

Switch on (float down)

Below 1 Ω

HINT:

If there is no problem after finishing the above check, adjust the brake fluid level to the MAX level.

NG

REPLACE BRAKE MASTER CYLINDER RESERVOIR SUB-ASSEMBLY

OK

7.

CHECK HARNESS AND CONNECTOR (COMBINATION METER ASSEMBLY - MASTER CYLINDER RESERVOIR SUB-ASSEMBLY)

(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 J28 combination meter assembly connector.

(c) Check both the connector case and the terminals for deformation and corrosion.

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

J28-14 (SW) - A3-1 (+)

Always

Below 1 Ω

J28-14 (SW) or A3-1 (+) - Body ground

Always

10 kΩ or higher

A3-2 (E) - Body ground

Always

Below 1 Ω

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

8.

READ VALUE USING TECHSTREAM (BRAKE WARNING LIGHT)

(a) Reconnect the A3 brake fluid level warning switch (brake master cylinder reservoir sub-assembly) connector.

(b) Reconnect the J28 combination meter assembly connector.

(c) Enter the following menus: Chassis / ABS/VSC/TRAC / Data List.

ABS/VSC/TRAC

Tester Display

Measurement Item

Range

Normal Condition

Diagnostic Note

Brake Warning Light

Brake warning light

ON or OFF

ON: Warning light on

OFF: Warning light off

-

(d) Check the Techstream display condition of the brake warning light.

Result

Proceed to

The value of Brake Warning Light is ON

A

The value of Brake Warning Light is OFF

B

A

REPLACE BRAKE ACTUATOR ASSEMBLY

B

INSPECT METER / GAUGE SYSTEM

    Brake Warning Light does not Come ON

    Open in ABS Motor Relay Circuit (C146C)

    See More:

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