SFI SYSTEM, Diagnostic DTC:P0504

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

DESCRIPTION

The stop light switch 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 and sets 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 intelligent tester, both the Data List items Stop Light Switch and ST1 are ON when the brake pedal is depressed because the characteristics of ST1 indication are the opposite of the Stop Light Switch indication.

DTC No.	DTC Detection Condition	Trouble Area
P0504	Conditions (a), (b) and (c) continue for 0.5 seconds or more (1 trip detection logic) (a) Engine switch on (IG) (b) Brake pedal released (c) STP signal OFF when ST1- signal OFF	Short in stop light switch signal circuit STOP fuse Stop light switch ECM

DTC No.

DTC Detection Condition

Trouble Area

P0504

Conditions (a), (b) and (c) continue for 0.5 seconds or more (1 trip detection logic)

(a) Engine switch on (IG)
(b) Brake pedal released
(c) STP signal OFF when ST1- signal OFF

Short in stop light switch signal circuit
STOP fuse
Stop light switch
ECM

WIRING DIAGRAM


*a	from Battery
*b	STOP
*c	from IG2 Relay Terminal 3
*d	Stop Light Switch Assembly

CAUTION / NOTICE / HINT

Tech Tips

Read freeze frame data using the intelligent tester. 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.

Read freeze frame data using the intelligent tester. 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.
Stop light switch conditions can be checked using the intelligent tester.

Connect the intelligent tester to the DLC3.
Turn the engine switch on (IG).
Turn the tester on.
Enter the following menus: Powertrain / Engine / Data List / Stop Light Switch and ST1.
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

CHECK HARNESS AND CONNECTOR (POWER SOURCE VOLTAGE)

*1 Front view of wire harness connector: (to Stop Light Switch)

Disconnect the A79 stop light switch connector.

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

Standard Voltage

Tester Connection	Condition	Specified Condition
A79-1 (B) - Body ground	Always	11 to 14 V

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

CHECK HARNESS AND CONNECTOR (POWER SOURCE VOLTAGE)

*1 Front view of wire harness connector: (to Stop Light Switch)

Disconnect the A79 stop light switch connector.
Turn the engine switch on (IG).

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

Standard Voltage

Tester Connection	Condition	Specified Condition
A79-5 (B) - Body ground	Engine switch on (IG)	11 to 14 V

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

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

*1 Front view of wire harness connector: (to Stop Light Switch)

Disconnect the A79 stop light switch connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
A79-3 (GND) - Body ground	Always	Below 1 Ω

REPAIR OR REPLACE HARNESS OR CONNECTOR

CHECK ECM (STP AND ST1- VOLTAGE)


*1	Brake Pedal Depressed
*2	Brake Pedal Released

Turn the engine switch on (IG)

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

Standard voltage

Tester Connection	Condition	Specified Condition
A14-12 (ST1-) - E3-1 (E1)	Brake pedal depressed	Below 1.5 V
A14-12 (ST1-) - E3-1 (E1)	Brake pedal released	7.5 to 14 V
A14-13 (STP) - E3-1 (E1)	Brake pedal depressed	7.5 to 14 V
A14-13 (STP) - E3-1 (E1)	Brake pedal released	Below 1.5 V

REPLACE ECM Click here

CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH - ECM)


*1	Front view of wire harness connector: (to Stop Light Switch)
*2	ECM Connector

Disconnect the A79 stop light switch connector.
Disconnect the A14 ECM connector.

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

Standard resistance (Check for open)

Tester Connection	Condition	Specified Condition
A79-2 (L) - A14-13 (STP)	Always	Below 1 Ω
A79-4 (L) - A14-12 (ST1-)	Always	Below 1 Ω

Standard resistance (Check for short)

Tester Connection	Condition	Specified Condition
A79-2 (L) or A14-13 (STP) - Body ground	Always	10 kΩ or higher
A79-4 (L) or A14-12 (ST1-) - Body ground	Always	10 kΩ or higher

REPLACE STOP LIGHT SWITCH ASSEMBLY Click here

REPAIR OR REPLACE HARNESS OR CONNECTOR