DTC P0504: Brake Switch Correlation: Description

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The cruise brake switch and the stop lamp switch are brake pedal inputs to the ECM to determine if the brake pedal is applied or released. Ignition voltage is supplied at the cruise brake switch input to the ECM whenever the ignition is turned on and the brake pedal is released (switch closed). If the brake pedal is applied, the cruise brake switch input at the ECM will go low. The ECM stop lamp switch circuit works the opposite. Battery voltage is supplied at the stop lamp switch input to the ECM whenever the brake pedal is applied (switch closed). If the brake pedal is released, the stop lamp switch input at the ECM will go low. If the stop lamp switch input at the ECM were to open, the switch input would read between 5-9 volts (ECM pull-up voltage). The ECM monitors both brake switches by making sure they both transition (one changes from high, while the other changes to low or vice versa) together within a certain amount time from each other. If one switch transitions and the other does not, then one of the two switches contains a circuit fault or is not adjusted correctly. DTC P0504 will set if the cruise brake or stop lamp switch input at the ECM changes state for a certain length of time while the other did not for a certain number of consecutive times in one ignition cycle.