DTC P1574: BRAKELIGHT Switch Circuit: Description
WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
This diagnostic test functions on the assumption that sudden decrease in a non-drive, wheel speed must be caused by a brake application. Non-drive wheel speed and brakelight switch status are supplied to the PCM through serial data from the electronic brake control Module (EBCM). If there is a 2.5 MPH (4 KM/H) or greater decrease of non-drive wheel speed in 0.4 seconds and a transition of the TCC or extended travel contacts of the TCC brake switch without a transition of the brakelight switch, DTC P1574 is set.