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. HINT:

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

Signals

Brake Pedal Released

In Transition

Brake Pedal Depressed

STP

OFF

ON

ON

ST1-

ON

ON

OFF

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) Ignition switch to the ON position

(b) Brake pedal released

(c) STP signal OFF when ST1- signal OFF

• Short in stop light switch signal circuit

• Stop light switch

• ECM

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