P0504 Brake Switch ‘A’ / ‘B’ Correlation - Automotive Repair Guides & Equipment

COMPONENT LOCATION

GENERAL DESCRIPTION

The Stop lamp switch signal is used for the Cruise Control, ABS-ESC, Shifter release as well as brake lights. The stop lamp switch consist of two seperate switches. One switch is open while the other switch is closed. When the brake pedal is not depressed, one circuit is system voltage while the other circuit is zero volts. When the brake pedal is depressed, the values of the two circuits are reversed. The ECM monitors the two signals and if it see both switches with the same value it will set the code.

DTC DESCRIPTION

The ECM checks out the signals from both Stop lamp switches. If both switches are High or Low voltage simultaneously, (more than 0.5 sec) the ECM sets P0504.

DTC DETECTING CONDITION

Item

Detecting Condition

Possible cause

DTC Strategy

Case1

Comparing 2 brake signals during driving

1.	Poor connection

2.	Open or short in Stop lamp switch

3.	Faulty Stop lamp switch

Case2

ECM detects stop lamp input signal when vehicle stops.

Enable Conditions

Case1

Engine works

Vehicle Speed Sensor is abnormal.

Engine works

Vehicle Speed Sensor is normal and Vehicle Speed is over 20kph dring 1sec or more.

Case2

Engine works

Vehicle Speed Sensor is normal and Vehicle Speed is over 20kph dring 1sec or more.

Threshold value

Case1

The one brake signal’s change duration when another signal has been changed > 0.5 sec

Case2

Vehicle speed < 3kph

Vehicle acceleration < -6kph/s

Stop lamp “OFF” and not changing of stop lamp signal for more 3

Diagnosis Time

Continuous

MIL On Condition

NO MIL ON(DTC only)

SPECIFICATION

Item	During taking off the brake	During stepping on the brake
Stop Lamp	0V	Battery voltage
Stop Lamp Switch	Battery voltage	0V

DIAGNOSTIC CIRCUIT DIAGRAM

SIGNAL WAVEFORM & DATA

Fig.1) Normal data of Brake Switch during brake pedal released after depressed.

MONITOR GDS DATA

1.	Connect GDS to Data Link Connector(DLC).

IG “ON”.

3.	Select “DTC” button, and then Press “DTC Status” to check DTC’s information from the DTCs menu.

4.	Read “DTC Status” parameter.

Is parameter displayed “Present fault”?

	▶ Go to “Terminal and Connector inspection” procedure.
	▶ Fault is intermittent caused by poor contact in the sensor’s and/or ECM’s connector or was repaired and ECM memory was not cleared. Thoroughly check connectors for looseness, poor connection, ending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary

TERMINAL AND CONNECTOR INSPECTION

1.	Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.

2.	Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.

Has a problem been found?

	▶ Repair as necessary and go to “Verification of Vehicle Repair” procedure
	▶ Go to ” Power Circuit Inspection ” procedure.

POWER CIRCUIT INSPECTION

■ Check voltage

1.	IG “OFF” and disconnect ECM connector.

2.	IG “ON” and keep the brake taking off. (Measurement “A”).

3.	Measure the voltage between brake switch signal terminal of ECM harness connector and chassis ground.

4.	Measure the voltage between brake lamp signal terminal of ECM harness connector and chassis ground .

5.	Keep the brake stepping on.(Measurement “B”)

6.	Measure the voltage between brake switch signal terminal of ECM harness connector and chassis ground.

Measure the voltage between brake lamp signal terminal of ECM harness connector and chassis ground .

B+

Item	During taking off the brake	During stepping on the brake
Stop Lamp	0V	Battery voltage
Stop Lamp Switch	Battery voltage	0V

Is the measured voltage within specification ?

	▶ Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair as necessary and go to “Verification of Vehicle Repair” procedure.
	▶ Go to “Check open in harness” as follows.

■ Check open in harness

1.	IG “OFF” and disconnect stop lamp switch and ECM connector.

2.	Measure the resistance between brake switch signal terminal of ECM harness connector and brake switch signal terminal of Stop lamp switch harness connector.

Measure the resistance between brake lamp signal terminal of ECM harness connector and brake lamp signal terminal of Stop lamp switch harness connector.

Below 1Ω

Is the measured resistance within specification ?

	▶ Go to “Check Battery voltage” procedure.
	▶ Repair open in circuit and go to “Verification of Vehicle Repair” procedure.

■ Check battery voltage

1.	IG “OFF” and disconnect stop lamp switch connector.

2.	Measure the voltage between power supply terminals of stop lamp switch harness connector and chassis ground.

IG “ON”

Measure the voltage between power supply terminals of stop lamp switch harness connector and chassis ground.

Specification :

Item	IG “OFF”	IG “ON”
Power supply to brake switch side	Battery voltage	Battery voltage
Power supply to brake lamp side	0V	Battery voltage

Is the measured voltage within specification ?

	▶ Substitute with a known – good stop lamp switch and check for proper operation. If the problem is corrected, replace stop lamp switch and go to “Verification of Vehicle Repair” procedure.
	▶ Check the fuse between battery and stop lamp switch. ▶ Repair open or short in power circuit of stop lamp switch

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