Lexus IS250 · Service Manual CRUISE CONTROL SYSTEM

P0571

Diagnostic trouble codes

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 of 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

E117774E03

INSPECTION PROCEDURE


1. READ VALUE ON 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 the brake pedal is operated, the display changes as shown above.



 OK
REPLACE ECM
NG


2. INSPECT STOP LIGHT SWITCH

  1. E117766E04
    Disconnect the stop light switch connector.

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

    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)

  1. E108173E04
    Measure the voltage according to the value(s) in the table below.

    Standard voltage:
    Tester Connection
    		 Condition
    		 Specified Condition
    A22-2 - Body ground
    		 Always
    		 10 to 14 V
    A22-3 - Body ground
    		 Engine switch on (IG)
    		 10 to 14 V



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


4. CHECK ECM

  1. E117777E02
    Reconnect the stop light switch connector.

  1. Disconnect the A5 and A6 connectors from the ECM.

  1. Turn the engine switch on (IG).

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

    Standard voltage:
    Tester Connection
    		 Brake Pedal Condition
    		 Specified Condition
    A6-4 (STP) - Body ground
    		 Depressed
    		 10 to 14 V
    A6-4 (STP) - Body ground
    		 Released
    		 Below 1 V
    A5-8 (ST1-) - Body ground
    		 Depressed
    		 Below 1 V
    A5-8 (ST1-) - Body ground
    		 Released
    		 10 to 14 V



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

REPLACE ECM


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