SFI SYSTEM, Diagnostic DTC:P0571

DTC Code DTC Name
P0571 Brake Switch "A" Circuit

DESCRIPTION

The stop light switch assembly is a duplex system that transmits two signals: STP and ST1-. These two signals are used by the ECM to monitor whether or not the brake system is working properly. If both signals, which indicate the brake pedal is being depressed or released, are detected simultaneously, the ECM interprets this as a malfunction in the stop light switch assembly and stores the DTC.

Tip:

The normal conditions are as shown in the table below. The signals can be read using the GTS.

Signal

Brake pedal released

In transition

Brake pedal depressed

STP

OFF

ON

ON

ST1-

ON

ON

OFF

  • [OFF] denotes ground potential.

  • [ON] denotes battery potential (+B).

  • On the GTS, both the Data List items Stop Light Switch and ST1 are ON when the brake pedal is depressed because the ST1 indication characteristic is opposite to the Stop Light Switch indication.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

MIL

Memory

P0571

Brake Switch "A" Circuit

  • Conditions (a) and (b) continue for 3 seconds or more (1 trip detection logic):

    • (a) Ignition switch ON

    • (b) STP signal off when ST1 signal off

  • Open or short in stop light switch signal circuit

  • Stop light switch assembly

  • ECM

Comes on

DTC stored

WIRING DIAGRAM

A326911E01

CAUTION / NOTICE / HINT

Note:

After replacing the ECM, perform idle learning.

Click here

Tip:

  • Read freeze frame data using the GTS. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

  • STP signal conditions can be checked using the GTS.

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Stop Light Switch and ST1.

    5. Check the STP signal when the brake pedal is depressed and released.

Brake Pedal Operation

Stop Light Switch

ST1

Depressed

ON

ON

Released

OFF

OFF

PROCEDURE

  1. READ VALUE USING GTS (STOP LIGHT SWITCH AND ST1)

    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Stop Light Switch and ST1.

      Powertrain > Engine and ECT > Data List

      Tester Display

      ST1

      Stop Light Switch

    5. Read the value displayed on the GTS.

      Standard

      Condition

      Specified Condition

      Brake pedal depressed

      ON

      Brake pedal released

      OFF

    Result

    Proceed to

    OK

    NG
    OK

    CHECK FOR INTERMITTENT PROBLEMS

    Click here

    NG

  2. CHECK STOP LAMP SWITCH ASSEMBLY INSTALLATION

    1. Check the stop light switch assembly installation.

      Click here

      Standard

      Stop light switch assembly is installed correctly.

    Result

    Proceed to

    OK

    NG
    NG

    SECURELY REINSTALL STOP LAMP SWITCH ASSEMBLY

    Click here

    OK

  3. CHECK TERMINAL VOLTAGE (POWER SOURCE OF STOP LIGHT SWITCH ASSEMBLY)

    A203090C19

    *a

    Front view of wire harness connector

    (to Stop Light Switch Assembly)

    1. Disconnect the stop light switch assembly connector.

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

      Standard Voltage

      Tester Connection

      Condition

      Specified Condition

      A20-2 - Body ground

      Always

      11 to 14 V

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - BATTERY)

    OK

  4. CHECK TERMINAL VOLTAGE (POWER SOURCE OF STOP LIGHT SWITCH ASSEMBLY)

    A203090C19

    *a

    Front view of wire harness connector

    (to Stop Light Switch Assembly)

    1. Disconnect the stop light switch assembly connector.

    2. Turn the ignition switch to ON.

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

      Standard Voltage

      Tester Connection

      Condition

      Specified Condition

      A20-4 - Body ground

      Ignition switch ON

      11 to 14 V

    Result

    Result

    Proceed to

    OK

    A

    NG (w/ entry and start system)

    B

    NG (w/o entry and start system)

    C
    B

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - IG2 RELAY)

    C

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - IGNITION OR STARTER SWITCH ASSEMBLY)

    A

  5. INSPECT STOP LAMP SWITCH ASSEMBLY

    1. Inspect the stop light switch assembly.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE STOP LIGHT SWITCH ASSEMBLY

    Click here

    OK

  6. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - ECM)

    1. Disconnect the stop light switch assembly connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance

      Tester Connection

      Condition

      Specified Condition

      A20-3 - A34-24 (ST1-)

      Always

      Below 1 Ω

      A20-1 - A34-40 (STP)

      Always

      Below 1 Ω

      A20-3 or A34-24 (ST1-) - Body ground

      Always

      10 kΩ or higher

      A20-1 or A34-40 (STP) - Body ground

      Always

      10 kΩ or higher

    Result

    Proceed to

    OK

    NG
    OK

    REPLACE ECM

    Click here

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR