Last Modified: 05-13-2024 6.11:8.1.0 Doc ID: RM100000002B522
Model Year Start: 2023 Model: Corolla Hatchback Prod Date Range: [03/2023 -           ]
Title: M20A-FKS (ENGINE CONTROL): SFI SYSTEM: P05042B; Brake Switch "A"/"B" Signal Cross Coupled; 2023 - 2025 MY Corolla Corolla Hatchback [03/2023 -        ]

DTC

P05042B

Brake Switch "A"/"B" Signal Cross Coupled

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 this DTC.

HINT:

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, Data List item Stop Light SW is ON when the brake pedal is depressed.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

MIL

Memory

Note

P05042B

Brake Switch "A"/"B" Signal Cross Coupled

Diagnosis condition:

  • Ignition switch ON

Abnormal condition:

  • STP signal OFF when ST1- signal OFF

Malfunction time:

  • 0.5 seconds or more

Trip logic:

  • 1 trip detection logic

Detection conditions:

  • Continuous

Sensors/components used for detection:

  • Stop light switch assembly
  • Open or short in stop light switch signal circuit
  • Stop light switch assembly
  • Instrument panel junction block assembly
  • ECM

Does not come on

DTC stored
  • SAE Code: P0504
  • DTC for Mexico Models: Applies

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

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

HINT:

  • 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 / Data List / Stop Light SW.
    5. Check the Data List indication when the brake pedal is depressed and released.

      Brake Pedal Operation

      Stop Light SW

      Depressed

      ON

      Released

      OFF
  • 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.

PROCEDURE

1.

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

*a

Front view of wire harness connector

(to Stop Light Switch Assembly)

(a) Disconnect the stop light switch assembly connector.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

A53-7 (B) - Body ground

Always

11 to 14 V
NG

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

2.

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

(a) Disconnect the stop light switch assembly connector.

(b) Turn the ignition switch to ON.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

A53-6 (B) - Body ground

Ignition switch ON

11 to 14 V

*a

Front view of wire harness connector

(to Stop Light Switch Assembly)
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - IGP-MAIN RELAY)
OK

3.

CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - BODY GROUND)

(a) Disconnect the stop light switch assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

A53-2 (GND) - Body ground

Always

Below 1 Ω
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

4.

CHECK TERMINAL VOLTAGE (STP AND ST1- VOLTAGE)

(a) Disconnect the ECM connector.

(b) Turn the ignition switch to ON.

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

Standard Voltage (for K120):

Tester Connection

Brake Pedal Operation

Specified Condition

A47-22 (ST1-) - Body ground

Released

7.5 to 14 V

Depressed

Below 1.5 V

A47-21 (STP) - Body ground

Released

Below 1.5 V

Depressed

7.5 to 14 V

Standard Voltage (for K121):

Tester Connection

Brake Pedal Operation

Specified Condition

A178-17 (ST1-) - Body ground

Released

7.5 to 14 V

Depressed

Below 1.5 V

A178-34 (STP) - Body ground

Released

Below 1.5 V

Depressed

7.5 to 14 V
OK

REPLACE ECM

NG

5.

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

(a) Disconnect the stop light switch assembly connector.

(b) Disconnect the ECM connector.

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

Standard Resistance (for K120):

Tester Connection

Condition

Specified Condition

A53-5 (L) - A47-22 (ST1-)

Always

Below 1 Ω

A53-3 (L) - A47-21 (STP)

Always

Below 1 Ω

A53-5 (L) or A47-22 (ST1-) - Body ground and other terminals

Always

10 kΩ or higher

A53-3 (L) or A47-21 (STP) - Body ground and other terminals

Always

10 kΩ or higher

Standard Resistance (for K121):

Tester Connection

Condition

Specified Condition

A53-5 (L) - A178-17 (ST1-)

Always

Below 1 Ω

A53-3 (L) - A178-34 (STP)

Always

Below 1 Ω

A53-5 (L) or A178-17 (ST1-) - Body ground and other terminals

Always

10 kΩ or higher

A53-3 (L) or A178-34 (STP) - Body ground and other terminals

Always

10 kΩ or higher
OK

REPLACE STOP LIGHT SWITCH ASSEMBLY

NG

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