DTC P0504-00: Brake Switch "A" "B" Correlation: General Description

The ECM uses brake signals to detect poor functioning of the ETC system. Two (brake light switch, brake test switch) signals are used to diagnose failure of the brake switch, and both signals transmit opposite values depending on brake application. With the brake not applied, the brake test switch transmits a power voltage, but the brake warning lamp switch outputs approximately 0V and outputs the opposite value when the brake is not applied with the brake is applied.