SFI SYSTEM, Diagnostic DTC:P0504

DTC Code DTC Name
P0504 Brake Switch "A" / "B" Correlation

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 the signals, which indicate the brake pedal is being depressed and released, are detected simultaneously, the ECM interprets this as a malfunction in the stop light switch assembly and stores the DTC.

Tech Tips

The normal signal conditions are as shown in the table below.

Signal (ECM Terminal) 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 Techstream, 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. DTC Detection Condition Trouble Area
P0504

Conditions (a) and (b) continue for 0.5 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

  • No. 1 integration relay

  • ECM

WIRING DIAGRAM

A011UZLE01
A011QZ5E01

INSPECTION PROCEDURE

Note

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

Tech Tips

  • Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. 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.

  • Stop light switch assembly conditions can be checked using the Techstream.

    1. Connect the Techstream to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the Techstream on.

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

    5. Check the Data List indication when the brake pedal is depressed and released.

      Brake Pedal Operation Stop Light Switch ST1
      Depressed ON ON
      Released OFF OFF

PROCEDURE

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

    1. Disconnect the stop light switch assembly connector.

      A011UGEE10

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

      Standard Voltage
      Tester Connection Condition Specified Condition
      A33-2 - Body ground Always 11 to 14 V
      Text in Illustration
      *a

      Front view of wire harness connector

      (to Stop Light Switch Assembly)
    NG

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

    OK

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

    1. Disconnect the stop light switch assembly connector.

      A011UGEE10

    2. Turn the ignition switch to ON.

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      A33-4 - Body ground Ignition switch ON 11 to 14 V
      Text in Illustration
      *a

      Front view of wire harness connector

      (to Stop Light Switch Assembly)
    NG

    CHECK HARNESS AND CONNECTOR (NO. 1 INTEGRATION RELAY - STOP LIGHT SWITCH ASSEMBLY) Click here

    OK

  3. INSPECT STOP LIGHT SWITCH ASSEMBLY

    1. Inspect the stop light switch assembly Click here.

    NG

    REPLACE STOP LIGHT SWITCH ASSEMBLY Click here

    OK

  4. CHECK TERMINAL VOLTAGE (STP AND ST1- VOLTAGE)

    1. Disconnect the ECM connector.

      A011U9ZE07

    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
      A25-24 (ST1-) - Body ground Brake pedal released 7.5 to 14 V
      Brake pedal depressed Below 1.5 V
      A25-11 (STP) - Body ground Brake pedal released Below 1.5 V
      Brake pedal depressed 7.5 to 14 V
      Text in Illustration
      *a Brake Pedal Depressed *b Brake Pedal Released
      *c

      Front view of wire harness connector

      (to ECM)

      		 - -
    NG

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

    OK

    REPLACE ECM Click here

  5. CHECK HARNESS AND CONNECTOR (NO. 1 INTEGRATION RELAY - STOP LIGHT SWITCH ASSEMBLY)

    1. Remove the No. 1 integration relay from the engine room relay block and junction block assembly.

    2. Disconnect the stop light switch assembly connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      1C-2 - A33-4 Always Below 1 Ω
      1C-2 or A33-4 - Body ground Always 10 kΩ or higher
    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

    REPLACE NO. 1 INTEGRATION RELAY Click here