Dtc P0571 Brake Switch A Circuit

Cruise Control System. Lexus Gs430, Gs300. Uzs190 Grs190
Cruise Control. Lexus Gs430, Gs300. Uzs190 Grs190

DESCRIPTION

WIRING DIAGRAM

INSPECTION PROCEDURE

READ VALUE OF INTELLIGENT TESTER

INSPECT STOP LIGHT SWITCH

CHECK WIRE HARNESS (STOP LIGHT SWITCH - BATTERY)

CHECK ECM

DTC P0571 Brake Switch "A" Circuit


DESCRIPTION

When the brake pedal is depressed, the stop light switch sends a signal to the ECM. When the ECM receives this signal, it cancels the cruise control. The fail-safe function operates to enable normal driving even if there is a malfunction in the stop light signal circuit. The cancellation condition occurs when voltage is applied to terminal STP. When the brake is applied, voltage is normally applied to terminal STP of the ECM through the STOP SW fuse and the stop light switch, and the ECM turns the cruise control off.

DTC No.
DTC Detection Condition
Trouble Area
P0571
Voltage of STP terminal and that of ST1- terminal on ECM are less than 1 V for 0.5 sec. or more
  1. Stop light switch
  2. Stop light switch circuit
  3. ECM

WIRING DIAGRAM


Lexus Gs430, Gs300. Uzs190 Grs190.Cruise Control.Cruise Control System. Dtc P0571 Brake Switch A Circuit


INSPECTION PROCEDURE

1.READ VALUE OF INTELLIGENT TESTER

  1. Connect the intelligent tester to the DLC3.

  1. Turn the engine switch on (IG), and turn the intelligent tester main switch ON.

  1. Check the Data List for proper functioning of the stop light switch.

    ECM (Cruise control):
    Item
    		Measurement Item / Display (Range)
    		Normal Condition
    		Diagnostic Note
    Stp Light SW M
    		Stop light switch signal (Main CPU) / ON or OFF
    		ON: Brake pedal depressed
    OFF: Brake pedal released
    		-
    OK:
    When brake pedal operation is performed, the result will be same as above.


OK
REPLACE ECM
NG


2.INSPECT STOP LIGHT SWITCH


    Lexus Gs430, Gs300. Uzs190 Grs190.Cruise Control.Cruise Control System. Dtc P0571 Brake Switch A Circuit

  1. Disconnect the stop light switch connector.

  1. Measure the resistance of the switch.

    Standard resistance:
    Tester Connection
    		Switch Condition
    		Specified Condition
    1 - 2
    		Switch pin not pushed
    		Below 1 Ω
    3 - 4
    		Switch pin not pushed
    		10 kΩ or higher
    1 - 2
    		Switch pin pushed
    		10 kΩ or higher
    3 - 4
    		Switch pin pushed
    		Below 1 Ω


NG
REPLACE STOP LIGHT SWITCH
OK


3.CHECK WIRE HARNESS (STOP LIGHT SWITCH - BATTERY)


    Lexus Gs430, Gs300. Uzs190 Grs190.Cruise Control.Cruise Control System. Dtc P0571 Brake Switch A Circuit

  1. Measure the voltage of the wire harness side connector.

    Standard voltage:
    Tester Connection
    		Condition
    		Specified Condition
    A37-2 - Body ground
    		Always
    		10 to 14 V
    A37-3 - Body ground
    		Engine switch on (IG)
    		10 to 14 V


NG
REPAIR OR REPLACE WIRE HARNESS AND CONNECTOR
OK


4.CHECK ECM


    Lexus Gs430, Gs300. Uzs190 Grs190.Cruise Control.Cruise Control System. Dtc P0571 Brake Switch A Circuit

  1. Reconnect the stop light switch connector.

  1. Disconnect the A6 and A7 ECM connectors from the ECM.

  1. Turn the engine suwitch on (IG).

  1. Measure the voltage of the wire harness side connectors.

    Standard voltage:
    Tester Connection
    		Brake Pedal Condition
    		Specified Condition
    A7-4 (STP) - Body ground
    		Depressed
    		10 to 14 V
    A7-4 (STP) - Body ground
    		Released
    		Below 1 V
    A6-8 (ST1-) - Body ground
    		Depressed
    		Below 1 V
    A6-8 (ST1-) - Body ground
    		Released
    		10 to 14 V


NG
REPAIR OR REPLACE WIRE HARNESS AND CONNECTOR (STOP LIGHT SWITCH - ECM)
OK

REPLACE ECM