DTC P0504-00: Brake Switch 'A'/'B' Correlation: 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 consists of two separate 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. If both switches have the same value it will set the code.