Brake Warning Light Remains ON: Wiring Diagram

WARNING: This page is about a different car, the 2006 Lexus IS 350. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Wiring Diagram

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NOTE: When replacing the skid control ECU, perform zero point calibration (See CALIBRATION ).

CHECK CAN COMMUNICATION SYSTEM

Check if the CAN communication system DTC is output (See DIAGNOSIS SYSTEM ).

Result

CONDITION CHART

Condition	Proceed to
DTC is not output	A
DTC is output	B

B : INSPECT CAN COMMUNICATION SYSTEM

A : GO TO NEXT STEP

CHECK MULTIPLEX COMMUNICATION SYSTEM

Check if the multiplex communication system DTC is output (See DTC CHECK/CLEAR ).

Result

CONDITION CHART

Condition	Proceed to
DTC is not output	A
DTC is output	B

B : INSPECT MULTIPLEX COMMUNICATION SYSTEM

A : GO TO NEXT STEP

CHECK IF SKID CONTROL ECU CONNECTOR IS SECURELY CONNECTED
1. Check if the skid control ECU connector is securely connected.
  OK: The connector should be securely connected.
NG : CONNECT CONNECTOR TO ECU CORRECTLY

OK : GO TO NEXT STEP
CHECK BATTERY
1. Check the battery voltage.
  Standard voltage:
  
  11 to 14 V
NG : CHECK AND REPLACE CHARGING SYSTEM OR BATTERY

OK : GO TO NEXT STEP

INSPECT SKID CONTROL ECU (IG1 TERMINAL)

Disconnect the skid control ECU connector.
Turn the engine switch on (IG).

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

Standard voltage

TESTER CONNECTION AND SPECIFIED CONDITION CHART

Tester Connection	Condition	Specified Condition
J77-1 (IG1) - Body ground	Engine switch on (IG)	10 to 14 V

Fig 2: Inspecting Skid Control ECU (IG1 Terminal)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG : REPAIR OR REPLACE HARNESS OR CONNECTOR (IG1 CIRCUIT)

OK : GO TO NEXT STEP

INSPECT SKID CONTROL ECU (GND TERMINAL)

Turn the engine switch off.
Disconnect the skid control ECU connectors.

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

Standard resistance

TESTER CONNECTION AND SPECIFIED CONDITION CHART

Tester Connection	Condition	Specified Condition
J78-26 (GND1) - Body ground	Always	Below 1 Ω
J78-14 (GND2) - Body ground	Always	Below 1 Ω
A35-22 (GND3) - Body ground	Always	Below 1 Ω

Fig 3: Inspecting Skid Control ECU (GND Terminal)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG : REPAIR OR REPLACE HARNESS OR CONNECTOR (GND CIRCUIT)

OK : GO TO NEXT STEP

INSPECT PARKING BRAKE SWITCH

Disconnect the parking brake switch connector.

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

Standard resistance

TESTER CONNECTION AND SPECIFIED CONDITION CHART

Tester Connection	Condition	Specified Condition
1 - Body ground	Parking brake switch ON (Switch pin free)	Below 1 Ω
1 - Body ground	Parking brake switch OFF (Switch pin pushed in)	10 kΩ or higher

Fig 4: Inspecting Parking Brake Switch

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG : REPLACE PARKING BRAKE SWITCH

OK : GO TO NEXT STEP

CHECK HARNESS AND CONNECTOR (SKID CONTROL ECU - PARKING BRAKE SWITCH)

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

Standard resistance

TESTER CONNECTION AND SPECIFIED CONDITION CHART

Tester Connection	Condition	Specified Condition
J77-14 (PKB) - A25-1	Always	Below 1 Ω
J77-14 (PKB) - Body ground	Always	10 kΩ or higher

Fig 5: Checking Harness And Connector (Skid Control ECU - Parking Brake Switch)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG : REPAIR OR REPLACE HARNESS OR CONNECTOR

OK : GO TO NEXT STEP

INSPECT BRAKE FLUID LEVEL WARNING SWITCH

Remove the reservoir tank cap and strainer.
Disconnect the brake fluid level warning switch connector.

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

HINT:

A float is placed inside the reservoir. Its position can be changed by increasing/decreasing the level of brake fluid.

Standard resistance

TESTER CONNECTION AND SPECIFIED CONDITION CHART

Tester Connection	Condition	Specified Condition
1 - 2	Float up (Switch OFF)	1.9 to 2.1 kΩ
1 - 2	Float down (Switch ON)	Below 1 Ω

Fig 6: Inspecting Brake Fluid Level Warning Switch

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 (BRAKE FLUID LEVEL WARNING SWITCH)

OK : GO TO NEXT STEP

CHECK HARNESS AND CONNECTOR (COMBINATION METER - BRAKE FLUID LEVEL WARNING SWITCH)

Disconnect the combination meter connector.

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

Standard resistance

TESTER CONNECTION AND SPECIFIED CONDITION CHART

Tester Connection	Condition	Specified Condition
J35-15 (SW) - A16-1 (+)	Always	Below 1 Ω
J35-15 (SW) - Body ground	Always	10 kΩ or higher
A16-2 (E) - Body ground	Always	Below 1 Ω

Fig 7: Checking Harness And Connector (Combination Meter - Brake Fluid Level Warning Switch)

NG : REPAIR OR REPLACE HARNESS OR CONNECTOR

OK : GO TO NEXT STEP

INSPECT COMBINATION METER ASSEMBLY
1. Perform Active Test of the combination meter (meter CPU) using the intelligent tester (See DATA LIST / ACTIVE TEST ).
  OK: The BRAKE warning light turns on or off in accordance with the intelligent tester.
  
  HINT:
  - Reinstall the connectors and restore the vehicle to its prior condition before checking the combination meter.
  - If troubleshooting has been carried out according to the Problem Symptoms Table, refer back to the table and proceed to the next step before replacing the part (See PROBLEM SYMPTOMS TABLE ).
NG : REPLACE COMBINATION METER ASSEMBLY

OK : REPLACE SKID CONTROL ECU